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Full text of "Geologic reconnaissance of the northern Coast Ranges and Klamath Mountains, California, with a summary of the mineral resources"

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PHYSICAL SCIENCES 
LIBRARY 

UC DAVIS 






Geologic Reconnaissance 

0£ t&e Tt&ttfan* (fawt ^cutyet and, 



California Division of Mines 

Bulletin 179 7960 



GEOLOGIC RECONNAISSANCE OF THE NORTHERN COAST RANGES 
AND KLAMATH MOUNTAINS, CALIFORNIA, WITH A 
SUMMARY OF THE MINERAL RESOURCES 



By WILLIAM P. IRWIN 
U. S. Geological Survey 
Menlo Park, California 



Bulletin 179 

CALIFORNIA DIVISION OF MINES 

FERRY BUILDING, SAN FRANCISCO, 1960 



tar*!' 
Est 

Pres 

Aft 

j 



STATE OF CALIFORNIA 

EDMUND G. BROWN, Governor 

DEPARTMENT OF NATURAL RESOURCES 

DeWITT NELSON, Director 

DIVISION OF MINES 

IAN CAMPBELL, Chief 

Bulletin 179 
Price $3.00 



Prepared cooperatively by the 
U. S. GEOLOGICAL SURVEY 

Publication authorized by the Director, 
U. S. GEOLOGICAL SURVEY 



CONTENTS 



Abstract 

Introduction 
Extent of area 
Previous work 
Present u ork 
Vcknow ledgments 
< ieograph; 



Page 
5 

9 
9 
9 

11 

11 

i: 



Paleozoic l>c-lt. Klamath 



( leologu foj mations 
Sedimentarj and volcanic rocks 
I'll Jurassic rucks 
Formations of the east< i n 
Mountains 
I ndifferentiated Paleozoic formations 
i . iplej greenstone 
Kennett formation 
Bragdon formation 
Formations of the central metamorphic licit. Klamath 
Mountains 
Abrams and Salmon formations 
Formations of the western Paleozoic and Triassic belt, 
Klamath Mountains 
Previous work 

I itliologj 

Vge Hi the rocks 
Formations oi Jurassic .mil Cretaceous 
Rocks (it middle Late Jurassic age 
tains 
Galice formation 

South Fork Belt of Diller I L903a), 
of Hershey (1906), and Kerr 
Manning and Ogle i L950) 

Rocks of late Late Jurassic and ( retai ■ age 

Strata along the west side of the Sacramento Valley 
Knoxville formation 

Shasta series 

Upper Cretaceous 
Rucks of the northern ("oast Ranges of California 
Franciscan formation of the central bell 
Metamorphosed Franciscan(P) formation of the 

eastern belt 

Coast. il belt "I undifferentiated sedimentarj rocks 
Cactaceous rocks in the Klamath Mountains province 
Uppermost Cretaceous sir.ua 
Yager formation of Ogle (1953) 



igi 

, Klamath Moun- 



14 
14 
16 

16 
16 



is 

18 
19 

20 

:i 



27 

27 



Weitchpec schist 

Ranch schist oi 



28 
SO 

;: 

33 

5 5 
34 

54 
54 

4: 

43 

44 
44 



( iualala series of Weave] (194 

( ',o\ eli i ilea 
Tertiary rocks 



Strata of I ocene age 
( n\ i In area 

Shasta Vallej an., i 



Strata of ( HigO( i 

Si i ii. i of Miocene age 

Point Arena area 

Covelo area 

( iarlierv illc area 

Petrolia area 



Winter formation oi Maxon 
Strata of Pliocene Igi 

Southern coastal area 

Wildcat group of Ogle I 1951 - 

I alor formation of Manning anil Ogle 

St. < ieorge formation 

Cache formation of \ndcrsoii (1936 

Volcanic rocks oi I ertiarj age 
Quaternarj rocks 

Marine sedimentarj deposits 

Continental sedimentary deposits 

Glacial deposits 

Volcanic rocks 

Landslide deposits 
Intrusive rocks 
< iranitic rocks 



Page 

44 
45 
46 
46 
46 
46 
46 
47 
47 
47 
4S 
ts 

48 
49 

49 
4" 



Ultramafic rocks 



Structure 



Mineral commodities 
Gold 
Platinum 
Chromite 
Copper 
Silver 

Quicksilver 
Manganese 

Miscellaneous metalliferous commodities 
Nonmetallic mineral commodities 
Gas and oil 
Coal 



References cited 



(1950)... 50 

51 
51 
51 

5: 

52 
52 
54 
55 

56 

56 

56 
56 



58 

64 
64 
67 
67 
69 
71 
71 
71 
71 
75 
75 
78 

78 



i :; 



CONTENTS— Continued 



Illustrations 



Plate 1. Geologic map of northwestern California .... In pocket 

Figure 1. .Map showing the relation of the report area to the 

major geologic provinces of California 8 



Index to topographic quadrangle maps of north- 
western California _ 



10 



J. Map of northwestern California and southwestern 
Oregon, showing distribution of lithic belts 1 5 

4. Diagram showing comparison of nomenclature used 

by Hershey (1901, 1906, and 1911), Maxson (1933), Phot< 

and Hinds (1932), for rocks that are at least in part 
equivalent to the rocks of the so-called southwestern 
Devonian and Carboniferous belts of Diller (1903a) 21 

5. Chart showing changes in concept of the Myrtle, 
Galice, and Dothan formations of Diller ( 1903b and 
1907) of southwestern Oregon, and correlations 
with the Franciscan, Knoxville, Horsetown, and 
Paskenta formations of northern California _ 40 

6. Graph showing trends of mineral production in 
northwestern California during the period 1880- 
1953 63 

7. Graph showing production of gold in northwestern 
California during the period 1903-1953 ._ 64 

8. Map of northwestern California showing location of 
lode deposits of gold — 65 

9. Map of northwestern California showing location of 
placer deposits of gold and platinum 66 

10. Map of northwestern California showing location of 
deposits of chromite 68 

1 1. Map of northwestern California showing location of 
deposits of copper ..._ - — ._ 70 

L2. Map of northwestern California showing location of 
deposits of quicksilver 72 



Page 

13. Map of northwestern California showing location of 
deposits of manganese 73 

14. Map of northwestern California showing location of 
deposits of miscellaneous mineral commodities _ 74 

15. Map of northwestern California showing location of 
deposits of limestone _ 76 

16. Map of northwestern California showing location of 
deposits of coal, and location of wells drilled for 
oil and gas (exclusive of the Sacramento Valley) ... 

1. Aerial view, looking west from near the eastern 
boundary of the Klamath Mountains province. . 13 

2. Aerial view, looking east toward the southern part 

of the Marble Mountains _. ._ _ 25 

.3. Distant view of the Coast Ranges ... 31 

4. Strike ridges of eastward-dipping strata of Jurassic 
and Cretaceous age 32 

5. Thin bedded shale, sandstone, and conglomerate of 
the Knoxville formation _ _ __ 33 

6. Quarry in eastward-dipping sandstone of Late Cre- 
taceous age 34 

7. Folded chert of the Franciscan formation _ 36 

8. Contorted greenschist of the metamorphosed Fran- 
ciscan(?) formation 39 

9. Thick beds of graywacke of the coastal belt ... 42 

10. Gualala series exposed in wave-cut cliff at Anchor 
Bay _ 45 

11. Lignite interbedded with light colored clay, silt- 
stone, and sandstone of the Weavcrville formation 47 



12. Anticline in strata of Miocene age . 

13. Strata of Pleistocene age 



... 48 
_ 53 

14. Aerial view of the Trinity Alps _ _ 55 

15. Debris flow in area of Franciscan formation .. 56 



(4) 



GEOLOGIC RECONNAISSANCE OF THE NORTHERN COAST RANGES 
AND KLAMATH MOUNTAINS, CALIFORNIA, WITH A 
SUMMARY OF THE MINERAL RESOURCES 

By WILLIAM P. IRWIN 

ABSTRACT 

This report describes the geology of northwestern California, an area of approxi- 
mately 19,000 square miles that includes most of the northern Coast Ranges and the 
Klamath Mountains geologic provinces in addition to the western part of the Sacramento 
Valley province. The text and maps are compilations of available published and un- 
published data, supplemented in large measure by reconnaissance during the period 
1953-1957 by members of the U. S. Geological Survey. 

The geologic provinces of northwestern California differ markedly from the stand- 
point of topography, geologic history, and mineral deposits. The Klamath Mountains 
province is an area of rugged mountains, with many peaks reaching an altitude of more 
than 6,000 feet and a few nearly 9,000 feet. Accordant ridges are conspicuous features, 
most commonly below 6,000 feet, and evidence of former glaciation is widespread in 
the higher parts of the mountains. The Klamath Mountains province is drained chiefly 
by the Klamath River and its tributaries, and by the Smith River. The drainage in general 
is from east to west, and cuts across the lithic and structural grain of the province. 
In contrast, the northern Coast Ranges are lower in general altitude, and only along 
the main divide between the Coast Ranges and the Sacramento Valley drainage do 
a few peaks reach as high as 6,000 feet and show evidence of former glaciation. The 
principal rivers of the northern Coast Ranges are the Eel, Mad, Van Duzen, and 
Russian. The general course of the drainage is parallel to the structural and lithic 
grain of the province and, with exception of the Russian River, is northwestward. The 
Russian River flows southeastward for much of its length. In the northern Coast Ranges, 
as in the Klamath Mountains, accordant ridges are abundant, but are generally at 
lower altitudes. 

The chief basis for defining the two provinces lies in a natural grouping of the 
principal rock units of each province with regard to intrusion by granitic rocks. The 
principal rock units of the Klamath Mountains range from early Paleozoic to middle 
Late Jurassic in age, and are intruded by granitic rocks that range from hornblende 
diorite to true granite in composition. In the northern Coast Ranges the principal rocks 
range from late Late Jurassic to Cretaceous in age, and there is little evidence that they 
have been intruded by granitic rocks. The principal rocks of both provinces, however, 
are intruded by abundant mafic and ultramafic rocks. 






The Klamath Mountains comprise four concentric, arcuate belts that are concave 
to the east. From east to west the belts are (1) the eastern Paleozoic belt, (2) the 
central metamorphic belt, (3) the western Paleozoic and Triassic belt, and (4) the western 
Jurassic belt. The formations of the eastern belt are well known, with the exception of 
the oldest unit which includes Silurian and perhaps even Ordovician rocks. The other 
formations are chiefly the Copley greenstone of Devonian age, the Kennett formation 
of later Devonian age, and the Bragdon formation of Mississippian age. The meta- 
morphic rocks of the central belt are mainly quartz-mica and hornblende schists of 
the Abrams and Salmon formations, and generally have been considered the oldest 
rocks of northwestern California. The western Paleozoic and Triassic belt includes mildly 
metamorphosed shales, sandstones, cherts, greenstones, and limestones. They have been 
studied little, and have been referred to variously as the Lower Slate and Blue Chert 
series, the southwestern Devonian and Carboniferous belts, the Chanchelulla forma- 
tion, and the Grayback formation. The extension of the belt into southwestern Oregon 
includes the Applegate group. The western Jurassic belt includes the Galice formation 
of middle Late Jurassic age, and mica schists and greenschist. The schists include the 
Weitchpec and Kerr Ranch schists, and the schists of South Fork Mountain. These schists 
generally have been correlated with the Abrams mica schist of the central metamorphic 
belt, but herein are described as metamorphic equivalents of the Galice formation. 

The northern Coast Ranges are chiefly graywackes and shales that range in age 
from late Late Jurassic to Late Cretaceous. Along a northwest-trending central belt, 
the graywacke generally contains little or potassium feldspar and is interbedded at 
many places with cherts and greenstones. This assemblage of graywacke, chert, and 
greenstone is referred to as the Franciscan formation, as it is similar to the Franciscan 
formation of the type area on the San Francisco Peninsula. Along the northern part 
of the east side of the central belt, the Franciscan formation is faulted against schist 
of the western Jurassic belt of the Klamath Mountains province. Along the southern part 
it is bordered by a wedge of mildly metamorphosed rocks, at least some of which are 
equivalents of the Franciscan of the central belt. The mildly metamorphosed rocks are 
separated from the Sacramento Valley sequence by a north-trending band of serpentine. 
A coastal belt of graywacke and shale lies west of the central belt of the Franciscan 
formation. These rocks are not, as is generally thought, part of the Franciscan formation, 
as the graywackes generally contain appreciable quantities of potassium feldspar, and 
as chert and greenstones are rare. 

The Sacramento Valley sequence is an orderly pile of graywacke, shale, and con- 
glomerate that has been subdivided into the Knoxville formation of late Late Jurassic 
(middle Tithonian) age, the Shasta series of Early Cretaceous age, and Upper Cretaceous 
rocks. The strata of the Sacramento Valley sequence contain appreciable quantities of 
potassium feldspar, bulkwise, and the average content increases from the oldest to 
the youngest rocks. In general the strata dip eastward, away from the Coast Ranges, 
and form conspicuous strike ridges that trend northward along the west side of the 
Sacramento Valley. The age of the Franciscan with respect to the Sacramento Valley 
sequence is not clearly known. On a paleontologic basis, the Franciscan seems to range 
from late Late Jurassic to Late Cretaceous in age, and thus to be an equivalent of 
the Sacramento Valley sequence. On other evidence, however, some of the Franciscan 
appears to be Late Jurassic in age, and older than the oldest strata of the Sacramento 
Valley sequence. 



(6) 



Marine sedimentary rocks that probably range in age from latest Cretaceous to 
early Tertiary occur in the northern Coast Ranges. These include the Yager formation 
near Cape Mendocino, unnamed beds near Covelo, and the Gualala series along the 
coast southeastward from Pt. Arena. The Gualala series lies west of the San Andreas 
fault, forming a northwesterly extension of the fault block bounded by the San 
Andreas and Nacimiento faults. 

Sedimentary rocks of Tertiary age occur in both the northern Coast Ranges and 
Klamath Mountains, and cover an extensive area underlain by the Jurassic and Cre- 
taceous strata along the west side of the Sacramento Valley. They range in age from 
Eocene through Pliocene. In the Coast Ranges they are chiefly marine in origin, whereas 
in the Klamath Mountains and Sacramento Valley they are mainly continental. Volcanic 
rocks of Tertiary age occur sparsely near Clear Lake in the report area, but they cover 
large areas southward in the Coast Ranges and eastward in the Cascade Range. 

Rocks of Quaternary age cover only a small percent of the area of northwestern 
California. They include valley fill, coastal and river terrace deposits, landslide debris, 
glacial deposits, and beach and dune sands. Volcanic rocks of Quaternary age are 
abundant in the report area only at Clear Lake in the northern Coast Ranges. 

The structure of northwestern California is highly complex and poorly known. In 
both provinces the strata most commonly dip eastward. In the northern Coast Ranges 
the principal structures appear to be northwest-trending strike-slip faults of the San 
Andreas system, and subparallel folds. The boundary between the Coast Ranges and 
western Klamath Mountains is a high-angle reverse fault that for much of its length 
is nearly parallel to the faults of the San Andreas system. The southern boundary of 
the Klamath Mountains province is a transverse fault that is aligned with major trans- 
verse faults in the Sacramento Valley and the Coast Ranges, and may be related 
technically to the Gorda submarine escarpment. The arcuate arrangement of lithic 
belts in the Klamath Mountains province is interpreted as resulting from forces from 
the east, and the boundaries between the lithic belts are thought to be chiefly reverse 
faults that dip eastward. 

Mineral commodities having a total value of approximately $150 million have been 
produced from the area since the middle 1800's. During the early days the production 
was chiefly metallic minerals, especially gold, but during recent years the production of 
nonmetallic mineral commodities such as sand, gravel, crushed rock, and natural gas 
has exceeded the value of the metallic minerals. Large quantities of gold have been 
produced from both placer and lode deposits, essentially restricted to the Klamath 
Mountains province. Chromite has been mined from areas of ultramafic rock, and about 
two-thirds of the production has been from the Klamath Mountains. Copper occurs in 
complex sulfide ores, and all but one of the deposits with a record of significant 
production are in the Klamath Mountains. Important quantities of quicksilver have 
been produced from several deposits in the Coast Ranges, and from one deposit in 
the Klamath Mountains. Many deposits of manganese occur in both provinces, but 
most of the small production has come from deposits in chert members of the Franciscan 
formation in the northern Coast Ranges. The production of gas and oil from strata of 
Tertiary age is becoming of increasing importance in the northern Coast Ranges in 
western Humboldt County. 



I 7 I 



California Division of .Minks 



I Bull. 179 



OREGON 



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Figure 1. Map showing the relation of the report area to the major geologic provinces of California. 






I960 I 



Northern Coasi R \\(.i s \m> ki \m \ i n .Mm \ i w\s 



INTRODUCTION 
Extent of Area 

The area described in this report (herein referred to 
as northwestern California) borders the Pacific coast for 
a distance of 250 miles from near the mouth of the Rus- 
sian River to the Oregon State boundary, and has an 
average width of about 75 miles. It is bounded on the 
cast for much of its length by the Sacramento Valley 
(fig. 1). The area includes Mendocino, Humboldt, Trin- 
ity, and Del Norte Counties, and parts of Sonoma, Lake, 
Glenn, Colusa, Tehama, Shasta, and Siskiyou Counties. 
Ir includes most of two geologic provinces, the northern 
Coast Ranges and the Klamath Mountains, and a narrow 
strip of the west side of the Sacramento Valley. 

Previous Work 

Northwestern California is, geologically, one of the 
least known areas in the State, although geologists have 
worked sporadically in it since the late 1 sod's. I he east- 
ern parr of the area, where economic interest was great- 
est, where fossils are most abundant, and where suitable 
base maps were available for plotting geologic data, was 
studied most intensively during the early days. The early 
work was largely done by J. S. Diller and (). 1 1. I lusho . 
although other early workers such as H. W. Fairbanks, 
Charles Schuchert, and J. P. Smith made notable con- 
tributions. 

Diller, of the U. S. Geological Survey, began work- 
ing in northwestern California and southwestern Oregon 
in 1883, and during the succeeding three decades he 
studied much of the northern Coast Ranges and Kla- 
math .Mountains. One of his early papers, published in 
1902, is a classic account of the physiographic develop- 
ment of the area, and provides the first clear definition 
of the two provinces. Perhaps his most important contri- 
bution, however, was a detailed study of the Redding 
30-minutc quadrangle in the eastern Klamath Mountains, 
where he worked out the stratigraphy ami named many 
of the formations. Diller's strarigraphic column has with- 
stood the test of time well and has required only minor 
modifications in later years. 

Hershey was an economic geologist who began exam- 
ining mineral deposits in the Klamath .Mountains province 
about 1 S97. During his field excursions throughout the 
province he also studied the regional geology, and in 
1901 he published the first comprehensive description of 
the geology of the Klamath .Mountains. In his report he 
named and described some of the principal formations. 
During the following decade, he published many papers 
expanding and modifying his earlier concepts. 

Between 1915 and World War II, reconnaissance map- 
ping was done at several places in the Klamath Moun- 
tains province. The geologic staff of the Southern Pacific 
Railroad mapped the area covered by the Etna and Vreka 
30-minute quadrangles (see Averill, 1931). Hinds (1933) 
prepared a map of the Weaverville and part of the Red 



Bluff JO-minute quadrangles, and Maxson i 1933) mapped 

much of Del Norte and part of western Siskiyou Coun- 
ties (in reconnaissance scale. 

Considerable geologic work was done by the staff of 
the I". S. Geological Survey timing the strategic min- 
erals investigations of World War II. Most of the work- 
was under the supervision of 1'. (.',. Wells, and was aimed 
chiefly at working out the geology of many small min- 
eralized areas. However, the area! mapping of broader 
areas in the Klamath Mountains of southwestern Oregon 
by Wells and others has led to a better understanding 
of the regional geology of the Klamath .Mountains of 
California. 

Since World War II, major contributions to the arcal 
geology have been made in the Redding area bv A. R. 
Kinkel, Jr.. J. P. Albers, and W. E. Hall (1956)', and in 
the Gasquet quadrangle, Del Norte County, by F. W. 
Cater. Jr., and F. G.Wells (1954). Heyl and Walker 
(1949) studied the limestone deposits of an area near 
Gazelle in eastern Siskiyou County. The geology of a 
small area along the upper reaches of Coffee Creek in 
I rinity Count) was mapped bj T. E. Gay < 1949). The 
Helena quadrangle in north-central Trinity Count) was 
mapped in detailed reconnaissance by I). P. Cox (written 
communication, 1956), and the Marble Mountain area in 
Siskiyou County by W. P. Pratt (written communica- 
tion, 1957). 

The western and southern part of the report area, the 
northern Coast Ranges of California, has been studied 
even less than the Klamath .Mountains. Reconnaissance 
trips were made in the northern Coast Ranges as early 
as the 1880's by J. 1). Whitney, G. F. Becker, H. W. 
Fairbanks, A. C. Lawson, and J. S. Diller. However, little 
arcal mapping has been done and, even today, our knowl- 
edge of the area is based largely on analogy with the 
central and southern Coast Ranges, anil with the west 
side of the Sacramento Valley, where formations similar 
to those of the northern Coast Ranges have been studied 
more intensively. 

During the past few decades important contributions 
to the arcal geology of the northern Coast Ranges have 
been made by many geologists, but the work has been 
chiefly adjacent to the southeast part of the present re- 
port area. Within the report area, the principal published 
contributions to the areal geology have been by Ander- 
son (1936), Clark (1940), Weaver (1943), MacGinitie 
(1943), .Manning and Ogle (1950), and Ogle (1953). 
W. B. Meyers has mapped the Wilbur Springs area (writ- 
ten communication, 1956), S. J. Rice has made a recon- 
naissance map of the Eureka, Trinidad, Orick, Klamath, 
and Crescent City quadrangles i written communication, 
1955), and C. G. Higgins has mapped the Pliocene rocks 
east of the San Andreas fault in northern Sonoma County 
(written communication, 1957). These previously un- 
published maps have been incorporated on the geologic- 
map of this report (plate 1). 









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12 



California Division of Mines 



[Bull. 179 



he and the writer jointly tested approximately 700 speci- 
mens of graywaeke from the northern Coast Ranges and 
Sacramento Valley for potassium feldspar content, and 
the results of the tests are used freely in this report. Pro- 
fessor H. E. Thalmann of Stanford University kindly ex- 
amined several thin sections of limestone for microfossils. 
The writer has also benefited through discussions with 
many other geologists, among them J. D. Frick of 
Humble Oil Co., G. Raydon and J. Floyd of Standard 
Oil Co., S. J. Rice of the California Division of Alines, 
D. Woods, D. M. Hill, and P. J. Lorens of the California 
Division of Water Resources, and J. E. Lawton and 
W. P. Pratt, graduate students of Stanford University. 
The writer has attempted to indicate faithfully the work 
of others at appropriate places in the text and on the map, 
but at some places may have failed where the overlap 
between map areas, or areas of thought, is indistinct. The 
field work was greatly facilitated by the friendly cooper- 
ation of the personnel of the U. S. Forest Service, espe- 
cially those stationed at Upper Lake Ranger Station. 

Geography 

Northwestern California has been divided into two 
provinces: the northern Coast Ranges in the southern 
and southwestern part, and the Klamath Mountains in 
the northeastern part (fig. 1). The boundary between 
the two provinces, as drawn by the writer, differs from 
the boundary originally drawn by Diller (1902, pi. 1). 
These provinces differ from one another in topography, 
in the character of the rocks, and to a large extent in the 
mineral resources. The northern Coast Ranges and Klam- 
ath Mountains constitute the major subject of this re- 
port, but parts of two other provinces are shown on the 
geologic map. A narrow strip of the Sacramento Valley 
along the east flank of the northern Coast Ranges is 
included because the geology along this strip is impor- 
tant to an understanding of the geology of the northern 
Coast Ranges. A part of the Cascade Range province is 
shown in the northeast part of the map. 

The Klamath Mountains province is an area of deeply 
trenched mountains in northwestern California and 
southwestern Oregon. In California, the province is 
drained by the Klamath and Smith Rivers. The Klamath 
River is the master stream of the province in California, 
and the Trinity, Salmon, and Scott Rivers are its major 
tributaries. The Trinity River, the largest tributary, 
drains the southern third of the area, and joins the Klam- 
ath River at Weitchpec near the middle of the western 
boundary of the province in California. The drainage 
pattern of the province is chiefly dendritic, and as most 
of the run-off is funneled into a single channel at 
Weitchpec, much of the drainage is transverse to the 
structural and lithic grain of the province. On the other 
hand, the structural and lithic grain of the province 
clearly controls certain parts of the major rivers in addi- 
tion to many tributary streams. The north-northwest 
trending lower part of the Trinity River and the South 
Fork of Trinity River are outstanding examples of such 



control, as are the Klamath River between Orleans and 
Happy Camp, and the South Fork of Smith River. 

The physiographic development of the Klamath Moun- 
tains and part of the northern Coast Ranges has been 
treated in detail by Diller (1894a, 1894b, 1902, and 1911). 
The following brief summary of Diller's views is given to 
provide the reader with a general impression of the phys- 
iography of the Klamath Mountains province, as well 
as to provide a convenient source of reference for later 
pages in this report. 

The altitude of many of the higher peaks in the Klam- 
ath Mountains is more than 6,000 feet, and a few peaks 
have an altitude of about 9,000 feet (photo 14). When 
viewed from a distance, the peaks are seen to project 
above even-crested and broad-topped ridges. The crest- 
lines of the ridges are accordant at two levels that range 
from about 500 to 1,000 feet apart, and they appear to 
be erosional remnants of two ancient land surfaces. The 
higher surface is known as the Klamath peneplain (Diller, 
1902, p. 15), and is considered (Diller, 1911, p. 12) to be 
the result of the first cycle of erosion in the development 
of the present landscape. The lower surface is known 
as the Sherwood peneplain (Diller, 1902, p. 22), and has 
resulted from a second cycle of erosion (Diller, 1911, 
p. 12). The second cycle consisted of rejuvenation of the 
streams, with subsequent deepening and widening of the 
valleys until a broad plain, the Sherwood peneplain, was 
formed. The subdued character of the landscape presum- 
ably was broken only bv the ridges on which the Klam- 
ath peneplain is preserved and from which the higher 
peaks projected. During the third cycle of erosion that 
has continued to the present, the streams were again 
rejuvenated by uplift, and by forming deep terraced 
canyons they have reduced the Sherwood peneplain to a 
succession of accordant ridges. 

The remnants of the Klamath peneplain, (photo 1) 
are not all at the same altitude. A reconstructed surface 
based on the remnants of the Klamath peneplain would 
gradually rise from north to south and from west to east. 
This is well shown by a remarkable ridge that marks the 
western and southern boundary of the Klamath Moun- 
tains in California, and whose crest is thought to be a 
remnant of the Klamath peneplain. The ridge is nearly 
continuous from the California-Oregon boundary to the 
western edge of the Sacramento Valley, except at a few 
places where it has been notched by major streams. In 
central Del Norte Count\- the crest of the ridge is at an 
altitude of about 2,500 feet. It gradually increases in 
altitude southeasterly until it attains an altitude of about 
6,000 feet in west-central Trinitv County where the ridge 
is known as South Fork Mountain. From the south end 
of the South Fork Mountains the ridge trends east-south- 
east, forming the southern boundary of the Klamath 
Mountains province, and along this part of the ridge the 
old surface in the vicinity of North Yolla Bolly Moun- 
tain is at an altitude of about 7,000 feet. Similar surfaces 
are found at an altitude of about 7,000 feet in the vicinity 
of the Trinity Alps north of Weaverville, but in the 



[9601 



North i u\ < ihm Rvm.is v\i> Kiwi a hi Moi\ivi\s 



13 




Photo I. Aerial view, looking west from near the eastern boundary of the Klamath Mountains province .1 few miles southeast of 
Gazelle. Siskiyou County. U.S. Highway 99 trends northward in the foreground. In the middle of the photo, the rocks to the right 
of center are mainly undifferentiated Paleozoic formations, chiefly of Silurian age; bold outcrops of light-colored limestone can be 
distinguished at a few places. A large area of ultramafic rock is to the left oi center. Part of the Scott Valley can be seen farther to 
the west. Remnants of the Klamath peneplain constitute the horizon. Photo GS-OAD, 1-22, August 1953. 



north-centra] pare of the province remnants oi the Klam- 
ath peneplain are at lower altitudes. The crests of the 
principal ridges between the Trinity Alps to the east and 
the South Fork Mountains to the west are remnants of 
the Sherwood peneplain (see Diller. 1911, fig. 1 I. 

I he northern Coast Ranges province consists domi- 
nantly of northwest-trending ridges that are approxi- 
mately parallel to the structural and lithic grain of the 
area. The longest and highest ridge, however, trends 
nearly north, from near Wilbur Springs in western Co- 
lusa County to the south end of the Klamath Moun- 
tains province, and is the drainage divide between the 
Sacramento Valley and northern Coast Ranges. It is con- 
sidered to be a southern continuation of the old surface 
developed by Diller's first cycle of erosion, as the crest 
of much of the ridge is locally broad and is generally 
between 5,000 and 6.(i()() feet in altitude as far south as 
Snow Mountain east of Lake Pillsbury. In the northwest- 
trending central part of the Coast Ranges, other ridges 
whose crests are thought to be remnants of the first cycle 
of erosion, as well as ridge-crests of the second cycle, 
are seen, although they are at lower altitudes than com- 
parable surfaces nearby in the Klamath Mountains. In a 
licit along much of the coast the crests of the ridges are 



generally at a common level that ranges between 1,000 
and 2,000 feet in altitude. 

The northern Coast Ranges are drained principal!) b) 
the Russian, Eel, Van Duzen, and Mad Rivers, as well as 
Redwood Creek and the extreme lower reaches of the 
Klamath and Smith Rivers. The drainage pattern is trel- 
lis, and although the major streams are chiefly parallel 
to the structural and lithic grain of the area, in some 
places thev are markedly transverse. The principal rivers 
drain northwestward. An exception is the Russian River 
which flows southeastward toward San Francisco I'.av 
for most of its length, but near Healdsburg it deviates 
sharply and flows southw estw ard, cutting across the 
grain of the Coast Ranges to discharge into the Pacific 
Ocean. 

The climate of northwestern California is determined 
mainly by westerly winds from the Pacific Ocean, and 
by the highland that includes the Klamath .Mountains and 
northeastern part of the ('oast Ranges. The average an- 
nual precipitation ranges from 30 inches in the southern 
parr of the area to more than 50 inches in much of the 
northern and western parts; locally it is as high as 100 
inches. During the late fall and winter months of heavy 
precipitation, the rivers become enormously swollen and 



14 



California Division of Mines 



Hull. 179 



often cause great damage to adjacent villages and trans- 
portation facilities. Rain is infrequent during the summer. 

The temperature along the coastal belt is moderate 
with small daily and annual ranges. Freezing is uncom- 
mon. The average annual humidity is greater than 70 
percent, and it decreases gradually toward the east. East 
of the coastal belt the climate is more rigorous, and is 
characterized by greater daily and annual ranges in tem- 
perature. In the higher country, snow flurries may be 
expected in late October, and during the winter much of 
the area above 4,000 feet is covered by snow. Patches of 
snow remain in some high protected areas until the mid- 
dle of summer, but most of the high country is suffi- 
ciently free of snow to permit field work in late May. 

Vegetation is dense throughout most of the area, and 
is especially lush along the coastal belt, where remarkable 
stands of redwood are found principally north of latitude 
40° N. Elsewhere, fir, spruce, pine, and cedar constitute 
the predominant forest cover. Brush and poison oak are 
abundant and are a deterrent to field work in much of the 
area. Lumbering is the principal industry throughout 
most of the area. 

The area contains about 40 percent of the State's water 
resources, but has only several percent of the State's irri- 
gable land. Most of the irrigable land is in the broad 
valleys near Eureka, Ukiah, Clear Lake, Willits, Covelo, 
and Potter Valley. Smaller openings in the forest cover 
found in the mountains, mainly in areas of landslide and 
solifluction along major shear zones, support a cover of 
natural grass for cattle grazing. 

Most of the land in the southern and coastal parts of 
the area is privately owned, except for a few State parks 
along the coast. Much of the land in the northern and 
eastern parts of the area, including Mendocino, Trinity, 
Six Rivers, and the Klamath National Forests, is Federally 
owned. Three large areas within the National Forests, 
the Marble Mountain, Salmon-Trinity Alps, and Yolla 
Holly-Middle Eel areas, have been designated officially as 
primitive areas. 

The principal highway through the area is U. S. Route 
101. The only paved roads that cross the area eastward 
to U. S. Routes 99 and 99W in the Sacramento Valley 
are State Route 20 from Ukiah to Williams, and U. S. 
Route 299 from Areata to Redding. State Route 1 fol- 
lows the coastline in the southern part and is connected 
to U. S. Route 101 by State Route 28. Secondary public- 
roads are mainly gravel and dirt, and in general are 
wide!)' spaced and furnish poor coverage of the area. 
Private logging roads as well as jeep trails lend additional 
accessibility to some of the more remote areas, but many 
large areas, particularly the three wilderness areas, are 
inaccessible by vehicle. The central part of the northern 
Coast Ranges from the San Francisco Bay area to Eureka 
is serviced by the Northwestern Pacific Railroad. 

GEOLOGIC FORMATIONS 

The distribution of the major geologic units is shown 
on the geologic map (pi. 1). .Most of these units have 



been studied only briefly by various geologists, and our 
meager know ledge of them precludes detailed descrip- 
tion of lithology, thickness of section, age, and relations 
to adjacent rocks. Few type sections have been described 
in detail or specifically located. Correlations of the princi- 
pal units with better-known formations elsewhere, or 
even within the area, is uncertain. Hence, some map units 
may consist of two or more formations that are somewhat 
similar in lithology but differ in age, and may more ac- 
curately be considered lithic units rather than forma- 
tional units. 

The geologic units of northwestern California include 
sedimentary and volcanic rocks of Paleozoic, Mesozoic, 
and Ce'nozoic age. Certain schists have been considered 
bv some geologists to be as old as Precambrian. The old- 
est paleontologically dated rocks are Silurian in age, and 
these may be the oldest rocks in the area. The Paleozoic 
and some Mesozoic rocks are intruded by ultramafic and 
granitic rocks. 

The pre-Tertiary rocks are readily differentiated into 
two groups on the basis of age, distribution, and relation 
to granitic rocks. The most significant point of division 
is between the middle Kimmeridgian and middle Titho- 
nian stages of the Upper Jurassic. The rocks of middle 
Late Jurassic (middle Kimmeridgian) and older ages are 
the principal formations of the Klamath Mountains prov- 
ince, and they have been intruded by abundant granitic- 
rocks. Those that range from late Late Jurassic (middle 
Tithonian) to Late Cretaceous in age are the principal 
units of the northern Coast Ranges and Sacramento 
Valley, and there is little evidence that they are intruded 
by granitic rocks. Some formations of both age divisions 
are intruded by ultramafic rocks. 

Sedimentary and Volcanic Rocks 

The pre-Tertiary sedimentary rocks of the area are 
chiefly marine sandstones and shales, and the sandstones 
are mostly the graywacke type. Rhythmically thin- 
bedded chert is abundant in some formations. Limestone 
forms perhaps only 1 percent of the formations of pre- 
Jurassic age, and is even less common in the formations 
of Jurassic and Cretaceous ages. Volcanic rocks of both 
andesitic and basaltic composition are present and are 
thought to be submarine flows and pyroclastics. They 
are mostly altered to greenstone, but locally structures 
showing their origin are preserved. 

The older pre-Tertiary sedimentary and volcanic rocks 
of northwestern California range from middle Late Juras- 
sic (middle Kimmeridgian) to Silurian and perhaps older. 
These rocks crop out only in the Klamath Mountains 
province, except for two areas of schist in the northern 
Coast Ranges near the western boundary of the Klamath 
Mountains province. The outcrop pattern of the older 
pre-Tertiary sedimentary and volcanic rocks of the 
Klamath Mountains defines a broad arc that is concave 
to the east. Within the arc are four rudely concentric 
irregular belts underlain by different lithic units (fig. 3). 
The western belt, along the western boundary of the 
province, consists of rocks thought to be chiefly middle 









19601 



Northern Coast Ranges vnd Klamath Mountains 



15 




Figure J. M.ip of northwestern California and southwestern 
Oregon, showing distribution of lithic belts. 



Late Jurassic (late Oxfordian to middle Kimmeridgian) 
in aye. I he three belts to the cast consist chief!) ol for 
mations of pre-Jurassic ages. 

In the southern part of the Klamath Mountains, the 
trend of the lithic belts is northwest; in the northwestern 
pari it is nearly north, and in the northeastern part it is 
northeast. In the Klamath .Mountains oi southwestern 
Oregon the trend is also northeast. I his arcuate, concen- 
tric arrangement of the formations of the Klamath Moun- 
tains will he referred to as the Klamath Mountains arc. 

Sedimentary strata that range from late I. ate Jurassic 
(middle Tithonian) to late Cretaceous in age are well 
exposed in orderl) sequence across a licit that trends north 
along the west side of the Sacramento Valley from near 
Wilbur Springs to the south end of the Klamath Moun- 
tains province. The strata have been grouped into the 
Knoxville formation of late I. ate Jurassic (middle Titho- 
nian) age. the Shasta series of Earl) Cretaceous age, and 
an unnamed unit of I. ate Cretaceous age. They appear 
to represent a nearly continuous record of deposition 
from late 1 .ate Jurassic (middle Tithonian) through much 
of the Late Cretaceous, and arc referred to herein as the 
Sacramento Valle) sequence. 

Sedimentary and volcanic rocks that range from late 
Late Jurassic (middle Tithonian) to Late Cretaceous in 
age occupy most of the northern Coast Ranges, and the 
formations occur chiefly in northwest-trending belts. The 
Franciscan formation is the principal unit of the northern 
Coast Ranges. Man) geologists consider the Franciscan to 
be restricted in age to Late Jurassic, but paleontologic 
evidence indicates that it may range in age from late Late 
furassic (middle Tithonian) to early Late Cretaceous 
(Cenomanian) and that it may be at least in part a fades 
of the Sacramento Valley sequence. A wide belt of sedi- 
mentary rocks that extends northwest along the coast 
from near the mouth of the Russian River to near Cape 
Mendocino, southwest of the area of the Franciscan for- 
mation, has previously been considered part of the Fran- 
ciscan formation, but in this report it is considered a 
separate unit. The rocks of the coastal belt arc at least in 
parr Cretaceous (Late Albian) in age. 

Formations of sedimentary rocks that are thought to 
be chiefly late Late Cretaceous in age, but may range into 
the early Tertiary, occur at several places in the northern 
Coast Ranges and at least one place in the Klamath 
Mountains. In the Coast Ranges these rocks are known 
as: the Gualala series, southwest of the San Andreas fault 
between Fort Ross ami Point Arena; the Yager formation 
of western Humboldt County, which is likely of similar 
age; and unnamed beds southwest of Covelo in central 
Mendocino County. Along the east side of the Klamath 
Mountains province, north of Shasta Valley, sedimentary 
rocks of Late Cretaceous age overlie granitic and pre- 
Jurassic rocks of the province. They have long been re- 
ferred to as the Chico formation, but recently have been 
named the Hornbrook formation (Peck and others, 
1956). 



16 



California Division of Minis 



[Bull. 179 



The Cenozoic rocks consist chiefly of the erosion prod- 
ucts of the pre-Tertiary rocks, but volcanic rocks of 
Cenozoic age are found at a few places in the report 
area, mostly in the vicinity of Clear Lake. The Tertiary 
sedimentary rocks are largely marine deposits in the 
northern Coast Ranges, and chiefly continental deposits 
in the Klamath Mountains and along the west side of 
the Sacramento Yallev. The Quaternary sedimentary de- 
posits are chiefly fluvial and lacustrine in origin, with 
the exception of small areas of marine terrace deposits 
along the coast. 

Pre-Jurassic Rocks 

Pre-Jurassic rocks occur only in the Klamath Moun- 
tains province, where they form the three eastern lithic 
belts of the Klamath Mountains arc; the fourth and west- 
ernmost belt consists chiefly of rocks of Late Jurassic age. 
The easternmost of the belts of pre-Jurassic rocks will 
be referred to simply as the eastern Paleozoic belt; the 
next belt to the west will be referred to as the central 
metamorphic belt; the third belt will be referred to as 
the western Paleozoic and Triassic belt (fig. 3). 

The eastern Paleozoic belt occupies the eastern side of 
the Klamath Mountains province and extends northward 
from the west side of the Sacramento Valley near Red- 
ding to the west side of Shasta Valley as far north as 
Yreka. Midway between Redding and Yreka, however, 
the continuity of the belt is disrupted by intrusive rocks. 
The rocks in this belt have been studied in greater detail 
than those in the other two belts of pre-Jurassic rocks, 
and are particularly well known in the vicinity of Red- 
ding, east of the report area. They have been divided 
into formations that range from Silurian to Mississippian 
in age. Generally they have been metamorphosed only 
near contacts with granitic intrusive rocks. 

The central metamorphic belt extends about 90 miles 
northward from a point southwest of Redding to Yreka. 
It averages about 10 miles in width. Two large areas of 
rocks similar to those of the central belt lie in Siskiyou 
County and southwestern Oregon within the general 
boundaries of the western Paleozoic and Triassic belt. 
The rocks of the central metamorphic belt include the 
Abrams and Salmon formations, which have long been 
considered to be the most ancient rocks of the Klamath 
Mountains province. They have been variously consid- 
ered to be of pre-Devonian, pre-Silurian, or possible even 
of Precambrian age. However, the possibility that they 
may be a metamorphic facies of formations of the eastern 
Paleozoic and western Paleozoic and Triassic belts has 
not been thoroughly explored. 

The western Paleozoic and Triassic belt adjoins the 
central metamorphic belt to the east, and is bounded to 
the west by the western Jurassic belt of the Klamath 
Mountains arc. The southern end of the belt is at the west 
side of the Sacramento Valley in northern Tehama 
County, and from there the belt trends northwestward 
through western Shasta and Trinity Counties, northward 
through western Siski) ou County, and northeastward 
through southwestern Oregon to near Tiller in Douglas 



County— a total distance of 180 miles. The belt has an 
average width of about 20 miles. The rocks of the west- 
ern Paleozoic and Triassic belt are similar to those of the 
eastern Paleozoic belt, except that they have been meta- 
morphosed weakly and are structurally more complex. 
Fossils found in the western Paleozoic and Triassic belt 
by the early workers were considered to range from 
Devonian to Carboniferous. However, re-examination of 
some of the earlv collections has shown that some of the 
socalled Devonian fossils are Triassic in age, and that 
some of the socalled Carboniferous are Permian. 

Formations of the Eastern Paleozoic Belt, 
Klamath Mountains 

The principal rocks of the eastern Paleozoic belt range 
from Silurian, or perhaps even Ordovician, to .Mississip- 
pian in age. They are described in this report as undiffer- 
entiated Paleozoic formations of Silurian and perhaps 
Ordovician age, the Copley greenstone of Middle Devo- 
nian age, and the Bragdon formation of probable Mis- 
sissippian age. The Kennett formation of Middle or early 
Late Devonian age is not known in the report area (pi. 1 ) 
but is described in this report because it is intimately as- 
sociated with the Copley greenstone and is exposed to 
the east nearby. 

Undifferentiated Paleozoic Formations. A large area 
between Scott Valley and Shasta Valley consists chiefly 
of undifferentiated formations of Paleozoic age. The pre- 
dominant rocks are shale, sandstone, chert, and limestone 
similar in appearance to the Kennett formation of De- 
vonian age, with which they generally have been cor- 
related. Recent paleontologic work (C. \Y. Merriam, 
oral communication, 1957) has shown that in part of the 
area the rocks are largely Silurian in age, and some per- 
haps Ordovician, and therefore not correlative with the 
Kennett formation. The rocks over most of the area, 
however, are poorly known, and formations known else- 
where in the eastern Paleozoic belt may be present. 

The undifferentiated Paleozoic formations have been 
studied in most detail by Heyl and Walker (1949) and 
C. W. Merriam (oral communication, 1957) near Gazelle, 
and by Brewer ( 1954) in the China Mountain quadrangle 
a few miles to the southwest. According to Heyl and 
^Yalker (1949, p. 517), the most prominent lithic unit 
in the Gazelle area is a fairly continuous thick-bedded 
limestone, about 200 feet thick, that forms bold cliffs 
(photo 1). The limestone is underlain by a sequence of 
somewhat slaty, gray and red shale, chert and sandstone, 
but in some places is separated from these rocks by con- 
glomerate containing abundant rounded pebbles of chert 
and quartz. The rocks that overlie the limestone are not 
well exposed, but are thought to be similar to the under- 
lying rocks. Strata similar to those of the Gazelle area 
are described by Brewer ( 1954, p. 10). The thickness of 
the stratigraphic section is not known. 

Heyl and Walker (1949, p. 517) state that ". . . in 
many places the bedding of the limestone is discordant 
with the strata immediately underlying it. Although this 
discordant contact might be interpreted as an erosional 



I960 



Northern Coasi Ranges \\i> Klamath Mountains 



r 



unconformity, field evidence suggests that locally fault- 
ing between the competent limestone and underlying in- 
competent strata took place ;ir the time oi regional fold- 
ing." In the China Mountain quadrangle, however, the 
slates that underlie the limestone are tightly folded and 
are intruded and altered by many dikes oi gabbro and 
diorite porphyry, yet the overlying limestone is neirher 
intruded no]- altered (Brewer, 1954, p. 11). 

I he rocks of the area of undivided Paleozoic forma- 
tions were briefly mentioned l>\ I [ershe) ( 1901a, p. 2 '2 ) 
as a northeastward extension of the Lower Slate scries he 
described more fully in Trinity and southern Siskiyou 
Counties, anil presumably he considered the Kennett for- 
mation a part of the same series. Diller (1903a, p. $46) 
included the strata in the vicinity of Gazelle in his so- 
called Northeastern Devonian belt of limestone and 
shales, a belt that includes the Kennett formation. Simi- 
larly, Brewer ( 1954) correlates the slate, chert, and lime- 
stone in China Mountain quadrangle with the Kennett 
formation, based on supposed similarities of lithology and 
age. 

Although present knowledge ot these rocks is slight, it 
indicates that much of the literature is erroneous regard- 
ing correlation of the rocks of the Gazelle area with the 
Kennett formation. L'nril recent years, the strata of the 
Gazelle area were considered to be of Devonian age 
(Diller, lS94b; Stauffer, 1930). However, according to 
paleontologic studies by C. W. Merriam (oral communi- 
cation. 1957; Merriam, L940, p. 44-4S; Westman, 1947) 
man} of the strata are ot undoubted Silurian age. al- 
though some Devonian and perhaps even Ordovician 
Strata are present. If the Kennett formation is Middle 
Devonian, an aye designation recently strengthened by 
the work of Kinkel, Mall, and Ubers (1956), many of 
the srrara of the Gazelle area obviousl) are not correlative 
with the Kennett formation. Brewer's correlation of 
rocks in the China Mountain area with those of the Ken- 
nett formation was based on a paper by Stumm ( 1954, p. 
223-224), who incorrectly assumed the Kennett forma- 
tion anil rocks of the Gazelle area to be correlatives and 
who redefined the age of the Kenncrt formation as Si- 
lurian on the basis ot tossils in rocks from the Gazelle 
urea. 

Copley Greenstone. The Copley greenstone is thought 
once to have overlain much or all of the area presently 
occupied b\ the Klamath Mountains (Hershey, 1901, 
p. 2.^2, and Minds, L932, p. >°4). Greenstones exposed 
widely throughout the eastern Paleozoic belt were named 
the Clear Creek formation by Hershey (190!, p. 226), 
and were later named Copley meta-andesite by Diller 
(1906). More recently, these rocks have been renamed 
Copley greenstone by Kinkel and Albcrs ( 1951, p. 4). 

The Copley greenstone consists of interlavcred spilitic 
volcanic flows, tuffs, and agglomerates that grade into 
rocks of andesitic and basaltic composition. Minor inter- 
beds of shale and chert are present. In the West Shasta 
district the formation is at least 3,700 feet thick, but the 
base is not exposed (Kinkel, Hall, and Albcrs, 1956). 



Elsewhere thicknesses of 1,200 and 1,500 feet have been 
reported (Hinds, 1933). last of the Sacramento River. 
beyond the report area, the Cople) is slightl) altered and 
sheared, bur it becomes progressively metamorphosed to 
the west, tow aril the Shasta Bally batholith. In tlie central 
"West Shasta district it is mostly altered to an albitc- 
chlorite rock, and farther west, where it is adjacent to 
the Shasta Bally batholith in the French Gulch quad- 
rangle, it is metamorphosed to amphibohte. epidote am- 
phibolite, hornblende gneiss, and migmatite over a width 
of as much as 4,000 feet | Kinkel. I [all, and Albcrs. 1956). 
The Coplej greenstone (Clear Creek formation) was 
first described bv Hershey (1901, p. 238) as Jurassic in 
age. owing to the intimate association of the greenstone 
with the overlying Bragdon formation, which he consid- 
ered equivalent in litholog) and age to the Mariposa 
slates of Jurassic age in the Sierra Nevada. Diller i 1906) 
assigned the Copley meta-andesite to the Devonian or 
older, for he found ir to be the oldest formation exposed 
in the Redding quadrangle and to be overlain by the 
Kennett formation of Middle Devonian age. In the Wesi 
Shasta district, according to Kinkel, Mall, and Albers 
(1956), "the Copley is believed to be Middle Devonian 
in aye, but no fossils have been found to accurately date 
it. It is conformable with the Balaklala rhyolite, and the 
upper part of the Balaklala has been dated as of Middle- 
Devonian age. 1 herefore, the main parr of the Copley 
is Middle Devonian or possibly slightly older." The 
Balaklala rhyolite occurs only locally, and conformably 
underlies the Kennett formation. 

The base ot rhe Coplev is not known in the eastern 
belt, rhe Copley is overlain conformably by the 
Balaklala rhyolite at a few places and at some places by 
the Kennett formation. .Most commonly, however, it is 
overlain by the Bragdon formation (Mississippian) with 
erosional unconformity (Kinkel, Mall, and Albers, 1956). 

Kennett Formation. The name Kennett formation 
was given by Smith ( 1 S94) for thin-bedded shale, sand- 
stone, chert, and limestone exposed along Backbone 
('reek near the abandoned town of Kennett north of 
Redding, east ot rhe area shown on the geologic map 
(pi. 1). 

1 he Kennett formation is missing from the strati- 
graphic section at many localities, and where present it 
ranges widely in thickness. Diller (1906) considered it 
to range from (I to 865 feet in thickness, and he attributed 
the marked range in thickness to uneven erosion of a for- 
merly continuous layer. Kinkel, Mall, and Albers i 1956) 
state that the maximum thickness is about 400 feet, and 
that rhe type section is thickened bv faulting. They at- 
tribute much of the uneven thickness of the Kennett to 
original variations in near-shore deposition of sediments 
against a. volcanic highland. 

Limestone of the Kennett formation occurs mainly as 
erosion remnants capping hills. Ir is fine grained, and 
ranges from thin to thick-bedded and light gray to 
bluish gray in color. According to Kinkel, Hall, and 
Albers i 1956) the limestone probably occurs at only one 



18 



California Division oi Minis 



Hull. 179 



horizon in the West Shasta district, and is a maximum of 
about 2nd feet thick. It is discontinuous because of fault- 
ing and erosion. 

On the basis of an abundant fossil fauna found in the 
limestone and calcareous shales, the age of the Kennett 
has been well established as late Middle or early Late 
Devonian (Diller, 1906. p. 2; Stauffer, 1930. p. 95, 96; 
and Kinkel. Hall, and Albers, 1956). 

According to Kinkel, Hall, and Albers ( 1956) the Ken- 
nett formation grades into the underlying Balaklala rhyo- 
litc, and where the Balaklala is not present the bedding 
of the Kennett is conformable with the underlying 
Copley greenstone. However, Hinds ( 1933, p. 90) states 
that the Kennett overlies deformed and eroded Copley 
greenstone. 

/;, agdon Formation. The Bragdon formation is widelv 
exposed in the eastern Paleozoic belt, and occurs in 
several relatively small areas within the general bound- 
aries of the central metamorphic belt. It was named by 
Hershe) I 1901, p. 226, 1904). and described as a ". . . se- 
ries of alternating thin-bedded black slates and thick- 
bedded, blue quartzites . . ." of Jurassic age (1901, p. 
2'S). Later it was studied in greater detail by Diller 
i 1903a, 1905, and 1906) and shown to be Paleozoic in 
age. 

The Bragdon consists of a monotonous sequence of 
interbedded shale, siltstone, sandstone, and conglomerate. 
Some of the sandstone shows graded bedding (Kinkel, 
Hall, and Albers. 1956). The sandstone grains consist 
chiefly of chert and quartz. Some of the sandstone is 
tufTaceous. 

The conglomerates are mostly pebbly, and the pebbles 
are mainly light-grav to black chert, shale, and vein 
iiu.ni/ i Kinkel. Hall, and Albers, 1956). Fragments of 
fossiliferous limestone are found in some of the coarser 
conglomerates, and these, as well as most of the Bragdon. 
are thought to have come from the Kennett formation 
(Diller, 1906). 

["he thickness of the Bragdon formation is difficult 
to determine, owing to an abundance of small folds, but 
may be as great as 6.000 feet (Diller. 1906). Partial sec- 
tions 5,500 and 1.450 feet thick have been measured bj 
Kinkel. Hall, and Albers ( 1956). 

I he age of the Bragdon formation is based partly on 
paleontologic evidence, but few fossils have been found. 
fossils found by the early workers (Diller. 1906) were 
thought likely to be Mississippian in age. Recent studies 
indicate that the age of the Bragdon formation may range 
from Devonian to Mississippian | Kinkel, Hall, and Albers. 
1956). The Bragdon sediments were deposited on the 
partly eroded Kennett formation of Middle or early Late 
Devonian age. but according to Kinkel. Hall, and Albers 
( 1956) the contact between the Bragdon anil Kennett 
formations is sharp and conformable at most places. In 
places where the Kennett was not deposited, or has been 
eroded completely, the Bragdon rests on the Balaklala 
rhyolite or the Copley greenstone. In the northwestern 
part of the Weavcrville 15-minute quadrangle (tig. 2). 



the Bragdon formation underlies an area of several square 
miles within the central metamorphic belt. There it is in 
contact with the Abrams formation, and with rocks of 
the western Paleozoic and Triassic belt, but the contact 
relations are not known. 

Formations of the Central Metamorphic Belt, 
Klamath Mountains 

The rocks of the central metamorphic belt are prin- 
cipally quartz-mica schists and hornblende and chlorite 
schists. Crystalline limestone and quartzite or meta-chert 
occur at some places in the quartz-mica schist. In the 
southern part of the belt, these rocks were named Abrams 
formation anil Salmon formation for exposures in the 
upper Coffee Creek area and along the higher reaches 
of the Salmon River, respectively (Hershey, 1901. p. 
226). The Abrams formation includes the quartz-mica 
schists and interlavered marble and quartzite or meta- 
chert. The Salmon formation includes the hornblende 
and chlorite schists, and commonly is considered to over- 
lie the Abrams formation conformably. Generally the 
two formations arc considered to be the oldest forma- 
tions of the Klamath .Mountains, and to be of pre-De- 
vonian, prc-Silurian, or possibly Precambrian age. How- 
ever, the ancient ages assigned to these formations seem 
to be based largely on the high metamorphic grade of 
these rocks relative to the lower metamorphic grade of 
the presumabl) younger rocks or adjacent belts. On the 
geologic map (pi. 1 ) the Abrams and Salmon formations 
are shown as a single unit. The most detailed descriptions 
of these formations are by Hershey (1901 ). Hinds ( 1932 
and 1935). and Gay ( 1949). 

Rocks somewhat similar to the Abrams and Salmon 
formations crop out in the northern part of the central 
belt, and in a large area isolated within the general bound- 
aries of the western Paleozoic and I riassic belt in Cali- 
fornia and southern Oregon. They commonly are referred 
to the Abrams and Salmon formations although they arc 
not known with assurance to be correlative. The large 
isolated area is chiefly north of the Klamath River, and 
covers the four common corners of the Seiad and Yreka 
30-minute quadrangles in California (fig. 2). and the 
Grants Pass and Vledford 30-minute quadrangles in 
southern Oregon. In the Seiad quadrangle the rocks have 
been referred to as "older metamorphic rocks" ( Rynear- 
son and Smith, 1940. p. 2X4). in the Yreka quadrangle as 
Abrams schist (see Averill, 1931. plate in pocket), and 
in the .Medford and Grants Pass quadrangles as "old 
schists'" (Wells and others, 1939 and 1940). The rocks 
of the large isolated area as a whole have been referred 
to as Salmon and Abrams schist by Wells and Cater 
(1950. p. si). In the Preston Peak quadrangle, isolated 
pendants of so-called Salmon formation have been re- 
ported by Maxson (1933, p. 12K). In the vicinity of 
Scott Valley, rocks previously mapped (see Averill. 1931, 
plate in pocket) as undivided sedimentary rocks and 
schists of early Paleozoic and possibly Precambrian age 
are considered to be Abrams and Salmon formations by 
Seymour .Mack (written communication. 1956). 



19601 



Northern Coasi Ranges vnd Kiwimh Mountains 



19 



I he schists ut' the South Fork Mountains and related 
ridges along the western boundary of the Klamath Moun- 
tains province generally have been correlated with the 
Abrams formation (see Diller, 1903a, p. 343; Maxson, 
1933, p. 128; Jenkins. 1938; and faliaferro and Hudson, 
1943, p. 219). but are herein correlated chiefly with the 
Galice formation. According to I liiuls i 1932, p. ^s" ), the 
Abrams and Salmon formations are exposed in rehama 
and Mendocino Counties, but cm the basis of the present 
reconnaissance, rocks of neither of these formations are 
thought tn lie exposed south of southern Shasta County 
where the) are overlapped by strata of the Sacramento 
Valley sequence. 

Abrams and Salmon Formations. The Abrams forma- 
tion consists principalis- of light to dark-graj quartz- 
mica schist. The schist is composed mostly of quartz, 
biotdte, and muscovite, with minor plagioclase and gar- 
net. According to Gaj (1949), the metamorphic grade 
of the schist is equivalent to ". . . the lower amphibolite 
facies and upper albite-epidote amphibolite facies "t re- 
gional metamorphism defined by Escola . . .". and to 
". . . the almandine /one of regional metamorphism de- 
fined b) Barrow and Tilley in the Scottish Highlands." 
Other rocks included in the formation are micaceous 
quartzites, pure quartzites, meta-conglomerates, and mar- 
ble. Some of the quartzite maj be crystallized chert. 
Hinds (1933) believes, as did Hershe) (1901, p. 228), 
that the Abrams formation is dominantly metamorphosed 
sedimentary rock; the mica schist was formed from class 
and shal) sandstones, and the quartzites from quart/ 
sandstones. He attributes the considerable thicknesses of 
interlayered quartzite and mica schist exposed along the 
Stunt Fork of the Trinity River to the metamorphism 
of thinly interbedded chert and clay. In general, the 
schistosit) of' the mica schist parallels the bedding. Rx - 
nearson and Smith ( 1940; also see Wells. Smith. R\ near- 
son, and Livermore, 1949. p. 23) sr.ue that in the Seiad 
quadrangle ". . . thin bands of nearly pure quartzite, 
which also lie parallel to the schistositv. suggests that 
the mica schists were derived from sands argillaceous 
sediments." 

Although the Abrams formation is chiefly mica schist 
that appears to base been formed from detrital and 
chemical sediments, hornblende schist that mas- be 
formed from volcanic rocks occurs locally in zones 
ranging from a few inches to several hundred feet thick: 
some of the /ones ol hornblende schist are concordant. 
but others appear to transgress the original bedding of 
the Abrams sediments i Hinds. 1933). Hinds interprets 
these /ones to represent intrusive phases of later (Salmon) 
volcanic activity, but recognizes the possibility that the 
concordant zones mas' represent contemporaneous vol- 
canism. 

The Abrams formation is 1,000 feet thick at the type 
locality in the upper Coffee Creek area, according to 
Hershey (1901, p. 228). Hinds < 1933) reports an incom- 
plete section 2,500 feet thick on the Stuart Fork of the 
Trinity Riser in the Weaverville 30-minute quadrangle 



(tig. 2), and a probable thickness of more than 5,000 feet 
in the southern part of the same quadrangle. The latter 
estimate of thickness is uncertain, owing to isoclinal 
folding (Hinds. 1933). 

I he Salmon formation consists dominantly of dark 
green hornblende schist and subordinate chlorite schist, 
and in some places contains interbedded calcareous and 
quartzitic meta-sediments. I he metamorphic grade of the 
Salmon formation is similar to that of the Abrams forma- 
tion (Gay, 194''. p. 2~). The schists are thought to have 
been formed from volcanic rocks, predominantlj mafic 
(loss s and p\ roclastic rocks, possibl) including sills and 
dikes in the Abrams formation (Hinds. 1932). 

According to Hershey (1901) the Salmon formation 
probably is not less than 2,500 feet thick. Hinds (1933, 
p. 83) reports that the greatest thickness exposed prob- 
ably exceeds 5,000 feet, but he is uncertain of that thick- 
ness owing to structural complications. Along the Scott 
Riser a fess miles southwest of Scott Bar, the thickness 
of the Salmoni"-) formation appears to be several thou- 
sand feet. 

Actinolite-epidote schist of the Salmon formation 
forms a remarkably uniform zone about half a mile xside 
along the north-trending, western boundars of the cen- 
tral metamorphic belt in the Helena quadrangle (fig. _ i. 
according to D. P. (lux (oral communication. 1956). To 
the ssest the actinolite-epidote schist presumably is in 
fault contact with mildls- metamorphosed sediments ol 
the western Paleozoic and Triassic belt; to the east it 
grades into fine-grained hornblende schist, and tinalls 
into coarse-grained hornblende schist ss ithin a distance 
of two miles of the fault contact. The foliation of the 
actinolite-epidote schist dips eastward at a moderate 
angle, and is crudely parallel to the bedding of the so- 
called Chanchelulla formation and to the foliation of 
the hornblende schist. 

Many large bodies of granitic rocks intrude both the 
Abrams and Salmon formations, and locally near the 
granite, migmatite and gneiss are formed. Hinds (1933, 
p. 82 ) states that in some areas the intrusion of granitic 
rock has caused remetamorphism of the Abrams forma- 
tion. Serpentini/cd ultramafic rocks arc in contact xs ith 
the schists, mostly along the eastern boundars of the belt. 
They are assumed to have intruded the Abrams and 
Salmon formations, although their contacts generally are 
sheared or concealed. In the northern part of the Seiad 
quadrangle. Wells. Smith. Rynearson, and l.ivermore 
( 1949) believe the serpentine to be essentially intrusise 
into the schists, and mention one small mass of coarsely 
recrs stallized schist enclosed in peridotite. 

Hershey < 1901 ) considered the Abrams formation to 
grade upxxard into the Salmon formation. Hinds i 1932, 
p. 390) agrees as to their relative stratigraphic positions. 
but contends that the rsso formations are separated by an 
erosional unconformity. Hossever. Gas i 1949. p. 27 
states that in the Coffee Creek area, the Abrams forma- 
tion appears to be younger than the Salmon formation, 
but that the evidence is not conclusive. 



20 



(Mil ORN1 V Dl\ ISION 01 VllNES 



Bull. L79 



The age of the Abrams and Salmon formations is un- 
known, us fossils have not been found in them, and as 
contact relations to strata of adjacent belts are obscure. 
1 [ershey ( 1901 ) considered the rocks to lie pre-Devonian, 
probably Algonkian, in age; Hinds | 1933, p. s4) believes 
them to be pre-Silurian. probably Precambrian in age. 
Both writers believed that the Abrams :\nd Salmon for- 
mations were metamorphosed and subsequently overlain 
with angular unconformity by rocks of Devonian or pre- 
Devonian age. Both have noted the striking difference in 
degree of metamorphism between the rocks (if the west- 
ern Paleozoic ami Triassic belt and those of the central 
metamorphic belt. Hinds reports finding pebbles and 
boulders of rocks similar to those of the Abrams and 
Salmon formations in the Chanchelulla formation oi the 
western belt, and J. P. AJbers (oral communication, 1957) 
states that fragments of simili.ir schists are found rarely 
in the Copies greenstone in the west Shasta district. 

The Abrams and Salmon formations generally are con- 
sidered distinctl) older than other formations of north- 
western California, and thought to have been metamor- 
phosed to then' present grade prior to the deposition oi 
the rocks known to be Paleozoic in age. The basic rela- 
tions, however, are so poorly known that the possibility 
that the Abrams and Salmon formations ma) be meta- 
morphic facies of adjacent formations of Paleozoic age 
should not be disregarded. The sandstones, slates, cherts, 
and limestones of the eastern Paleozoic and western 
Paleozoic and Triassic belts, in some places interlayered 
or intruded by greenstone, are suggestively similar to the 
lithic prototypes that have been postulated for the 
Abrams formation. Similarly, metamorphism of the 
Copley greenstone apparent!) results in rocks like those 
of the Salmon formation. 

.Metamorphic rocks similar to those of the Salmon for- 
mation are known to have formed from the Cople) 
greenstone on the east side of the Shasta Ball) batholith 
in southern Shasta Count) . 1 he) are best seen on Brandy 
Creek in the French Gulch quadrangle (fig. 2). where 
according to Kinkel. Hall, and AJbers I 1956) the Cople) 
greenstone has been metamorphosed to amphibolitc. 
hornblende gneiss, anil migmatite along a /one as much 
as 4,0(10 feet wide adjacent to the batholith. 1 linds i 1933, 
p. 87-88) slates that "along shear /ones and near the con- 
tacts with the large subjacent intrusives. the Copley v ol- 
canics have been again re'crystallized to chlorite ,m^\ less 
commonly hornblende schists. Hie latter in man) places 
are difficult to distinguish from the Salmon schists pre- 
viously described and a careful study of the stratigraphy 
or tracing of the schists into normal Copley rocks is nec- 
essarv for their correct identification." Hornblende and 
chlorite schists w est of the Shasta Bally batholith. but 
separated from the batholith by a narrow band of ultra- 
mafic rock, are regarded as Salmon formation i Hinds. 
1933, pi. 3) of ancient age. One may wonder, however, 
whether the schists on both sides of the batholith are not 
of the same w^q. 



I lershev i 1901, p. 239-243) discussed bi rejected the 
hypothesis that the Abrams and Salmon irmations arc 
more highlv metamorphic facies ot the so lied Devono- 
Carboniferous (lower Slate series), that rocks "t the 
western Paleozoic and [riassic belt. 1 be isative agents 
he discussed are intrusions of periodtit ir bodies of 
granitic rock, or the ". . . action ot a Lit magma of 
fluid granitic material underlying the whole tcrri- 
torv . . .". Kinkel. Hall and Albers (1 ( i) relate the 
metamorphism of the Cople) greenstone irectl) to the 
intrusion oi the batholithic rocks, but it questionable 
whether igneous intrusion can be the it to ac- 

count for the metamorphism ot the \br.u- and Salmon 
formations. The /ones of schist known . have been 
formed by metamorphism of Cople) ne occur 

as relatively narrow bands in a general art of nonmeta- 
morphosed rocks, whereas the \brams an Salmon for- 
mations form a belt 10 miles wide in w hb metamor- 
phism has been pervasive. I arge areas of itrusive rock 
are exposed along the central belt ot metamrphic rocks, 
and although one might postulate that the ire onl) the 
upward extension of ,\f\ enormous underlyig batholith. 
they do not satisfactoril) account for ti apparently 
rather uniform grade of metamorphism troughout the 
central metamorphic belt. 

\ stud) of the contact relations bei \br.mis 

anil Bragdon formations in the northwestei part of the 
Weaverville 15-minure quadrangle ma) prve of value 
in establishing a minimum age for the A bran formation. 
if the Bragdon formation proves to have ben deposited 
on the rocks of the central metamorphic be see pi. 1 ). 

Formations of the Western Paleozoic and Trissic 
Belt, Klamath Mountains 

The rocks of the western Paleozoic and riassic belt 
are chiclly slat) detrital sedimentary rocks, hert, lime- 
stone, and volcanic rocks. 1 he limestone is ist abund- 
ant and tonus discontinuous bodies along rue Iv -defined 
/ones within the western belt. 1 be trends i ones 

containing limestone bodies are roughl) pa] lei to the 
broad outlines of the western belt, and th trends, in 
addition to sparse paleontologic data, SUggfl that the 
structures .mA distribution of the formatias also are 
roughly parallel. I he rocks probablv const;. tc several 
straiigraphic units, some of which likely wil Move cor- 
relative with formations of the eastern Pa: zoic belt; 
however, they could not be divided into forrntions dur- 
ing the present brief reconnaissance, owing l part to 
their structural complexity. Their ages are porl) estab- 
lished, but they are least known to be rtlv late 
Paleozoic and Triassic in California, and parti) ["riassic in 
Oregon. In California the rocks of the wester Paleozoic 
and I riassic belt prcvioiislv have been descried as the 
Lower Slate series and Blue Chert series illcicv. [901 
and 1906), the so-called southwestern Devnian and 
southwestern Carboniferous belts (Diller, 103a), the 
Chanchelulla formation (Hinds. 1932), and the Jrayback 
formation (Maxson, 1933); in southwestern ( gon the 



I960! 



Northern Coast Ranges and Klamath Mountains 



21 



Sout h astern 
man 
elt 


Southwestern 

Carboniferous 

belt 


g 


Blu Chert Lower Slate 

s es series 
of s-called of so-called 

man rDevono- Carboniferous 
ge oge 
1 


ft> 

•-< 


i 

G r v b a c k | 

ition | 

of - called | 

Deon i a n | 

ge | 

1 


2 

a 

X 

VI 

O 

ID 


1 

1 Chanchelulla 
1 formation of 
1 so-called pre- 
1 Copley greenstone 

(Devonian) age 
1 


X 

D 

a. 
in 



Figure 4. l)i;i .mi showing comparison of nomenclature used 
by Hershej 1906, and 1911). Maxson (1933), and Hinds 

(1932), for rockshat arc at least in part equivalent to the rocks 
of the so-called mthwestern Devonian and Carboniferous belts 
of Diller (19 

rocks of the elt are known as the Applegate group 
(Wells, Hot/., id Cater, 1949) (fig. 4). 

Rocks near! equivalent in metamorphic grade to the 
Abranis and Simon formations occur in some areas of 
the northern : rt of the western Paleozoic and Triassic 
belt, and arc irerspersed with isolated areas of Abrams 
and Salmon f< mations. These are thought to be meta- 
morphic facie of the other rocks of the belt; in Oregon 
they are condered to be metamorphosed Applegate 
group (Wells 1955). 

Previous li rk. The first general description of the 
rocks of the stern Paleozoic and Triassic belt was by 
Hershey (19C). He proposed the name Lower Slate 
series for cm ures along the eastern part of the belt 
in western SI a, cistern Trinity, and southern Siskiyou 
Counties. He described the Lower Slate series (1901, 
p. 231-232 i a succession of black slates, quartzites, and 
limestones tin lie in a belt that is adjacent to the western 
edge of the cntral metamorphic belt and that extends 
from the \\ c side of the Sacramento Valley into Sis- 
kiyou Count ". . . it is traversed by the south fork 
of the Salmot River below Cecilville, where much of the 
country ovei width of ten or fifteen miles belongs to 
this series. Tfe belt averages about five miles in width." 
Continuing nrtheastward from the Salmon River, how- 
ever. Hershi included the rocks of the area of un- 
differentiate 'aleozoic formations with his Lower Slate 
series, that is le included rocks of the eastern Paleozoic 
belt that are parated from rocks of the western Paleo- 
zoic and Tn sic belt by metamorphic rocks of the cen- 
tral belt. 



In a later paper (1906, p. 59), Hershey applied the 
name Blue Chert series to "... a great series of black 
shales, limestones and blue cherts . . ." exposed on the 
western flank of Orleans Mountain a few miles east of 
Orleans in northeastern Humboldt County, and west of 
Hoopa Yallev "a great complex of intruded igneous ma- 
terial and of shales, bedded blue cherts and limestone 
identical in character with the Blue Chert series . . ." 
begins "... as a narrow belt and extends southward, 
gradually widening, to the border of the Sacramento 
Valley." On a reconnaissance map (1911), Hershey indi- 
cated a continuation of so-called Devonian (?) rocks, 
presumably the Blue Chert or Lower Slate series, north- 
w aid from near Orleans to the Oregon border of eastern 
Del Norte and western Siskiyou Counties. Hershey. 
strangely, does not mention the Lower Slate series in his 
paper of 1906, and owing to the coincidence of some 
areas vaguely described as the Lower Slate series in 1901 
and as the Blue Chert series in 1906, (compare 1901, p. 
232, and 1906, p. 60, 61), the relation between the Lower 
Slate series and Blue Chert series is not clear. However, 
the two series apparently included essentially all of the 
strata of the western Paleozoic and Triassic belt, with 
the exception of volcanic rocks that may be correlative 
with Copley greenstone. Hershey considered the Lower 
Slate series to be Devono-Carboniferous in age, and the 
Blue Chert series to be Devonian in age, based largely 
on paleontologic evidence gathered by Diller (1903a). 

Diller (1903a) collected fossils from widely-spaced 
bodies of limestone in the southern part of the western 
Paleozoic and Triassic belt, and briefly described the 
lithology at some of the localities. He concluded that the 
limestone bodies occur in two belts, referred to as the 
southwestern Devonian belt and the southwestern Car- 
boniferous belt (Diller, 1903a, p. 344, 348). Diller traced 
the so-called southwestern Devonian belt along the south- 
west side of the western Paleozoic and Triassic belt from 
near the west side of the Sacramento Valley to west of 
I Ioopa Valley. The so-called southwestern Carboniferous 
belt was traced through the central part of the western 
Paleozoic and Triassic belt to the northern half of the 
Ironside Mountain quadrangle (fig. 2) north of the 
Trinity River. Diller' s so-called southwestern Devonian 
belt apparently corresponds roughly to Hershey's Blue 
Chert series, and his so-called southwestern Carbonifer- 
ous belt is approximately equivalent to the Lower Slate 
series. 

In the extreme southeastern part of the western Paleo- 
zoic and Triassic belt. Hinds named the rocks the Chan- 
chelulla formation for ". . . excellent exposures on the 
slopes of a mountain of that name in the northwest cor- 
ner of . . ." the Chanchelulla Peak quadrangle (fig. 2) 
(Hinds, 1932, p. 392). "The base of the sequence is com- 
posed largely of thinly bedded gray or black cherts. 
which have suffered extensive recrystallization to quartz- 
ites. Interbedded with the cherts are micaceous and 
graphitic schists, quartzites, metaconglomerate and 
marble, some of which is graphitic. Toward the top of 



22 



California Division oi Minis 



Bull. 179 



the formation, the proportion of metamorphosed elastics 
and limestone is considerably greater though chert con- 
tinues as an important element." The formation is de- 
scribed as forming a broad belt that extends northwest- 
w ard from the edge of the Sacramento Valley through the 
Weaverville and Big Bar quadrangles. Although Hinds 
(1932, p. 392) states that the rocks of the Chanchclulla 
formation have not been described in previous literature, 
they apparently had been included as part of the Lower 
Slate series by Hershey and the so-called southwestern 
Carboniferous belt by Diller. 

In western Siskiyou County the western Paleozoic and 
Triassic belt includes the Grayback formation named by 
Maxson (1933, p. 128) in the Preston Peak quadrangle. 
The Grayback formation consists of rocks formerly 
mapped as Devonian(r) by Hershey (1911), and pre- 
sumably considered a northward continuation of the so- 
called southwestern Devonian belt (Diller and Kay, 1909, 
p. 50, 51). In the Seiad quadrangle, the rocks of the west- 
ern Palezoic and Triassic belt have been referred to as 
"younger metamorphic rocks" by Rvnearson and Smith 
('l 940,^-40). 

The western Paleozoic and Triassic belt has been 
studied mostly in southwestern Oregon. Diller made a 
reconnaissance of the area, and collected fossils from 
limestone localities (Diller and Kay, 1909). Later, the 
rocks of the belt in southwestern Oregon were mapped 
by Wells and others (1939, 1949), and by Wells, Hotz, 
and Cater ( 1949) who named them the Applegate group. 

Lithology. The western Paleozoic and Triassic belt 
consists dominantly of weakly metamorphosed detrital 
sedimentary rocks, chert, limestone, and volcanic rocks. 
The detrital sedimentary rocks are chiefly fine-grained 
and are altered to slate. Slate and chert constitute the 
bulk of the belt. Locally the volcanic rocks are abundant, 
and seem most abundant and diverse in the central and 
western pans of the belt. Generally they are altered to 
greenstone, and although some of the greenstone un- 
doubtedly is metamorphosed effusive volcanic rock in- 
terbedded with the slate and chert, some may be intru- 
sive. Most of the limestone is coarsely rccrystallized. 
Although limestone accounts for perhaps no more than 1 
percent of the area of outcrop of rocks of the western 
Paleozoic and Triassic belt, it likely will prove of con- 
siderable importance to an understanding of the stratig- 
raphy and structure of the Klamath .Mountains. It is the 
only rock of the western belt in which diagnostic fossils 
have been found, and ultimately it may provide useful 
marker horizons. 

The slate is a dark gray, fine-grained foliated rock, 
and much of it more properly might be referred to as 
phyllite, as the surfaces of foliation have a slight sheen 
apparently caused by the development of fine-grained 
micaceous minerals. Locally the rock is schistose. Gen- 
erally the foliation of the slate is nearly parallel to the 
bedding. 

Medium- to coarse-grained detrital rocks are seen at 
relatively few places throughout the southern half of the 



belt, but in the northern part of the belt, particularly in 
Oregon, they are more abundant. Hershev (1901, p. 2.31) 
listed quartzitc, along with slate and limestone, as an im- 
portant constituent of the Low er Slate series, but he evi- 
dently referred to meta-chert rather than sandstone. 
Hinds (1932, p. 392) mentions quartzite and metacon- 
glomerate interbedded with chert, schist, and marble in 
the power part of the Canchelulla formation at the type 
locality, and states that the proportion of metamorphosed 
elastics is greater in the upper part. Cox (oral communi- 
cation, 1956) found no metaconglomerate in the Helena 
quadrangle (fig. 2), but found one small outcrop of gray 
medium-grained quartzite. The quartzite consists chiefly 
of quartz grains, with a few chert fragments and a few 
percent of microcline and plagioclase feldspar. Similiar 
light-grav quartzite was seen by the writer only as sparse 
float near the head of the East Fork of Horse Linto 
Creek in the northwestern part of the Ironside .Mountain 
quadrangle (fig. 2). Conglomerates were not seen by the 
writer in the southern half of the belt, except for chert- 
rich pebble conglomerates at a few places along the west 
edge of the belt, particularly in the northeastern part of 
the Pilot Creek quadrangle. Coarse-grained, poorly sorted 
clastic rocks of volcanic affiliation crop out in the central 
and western part of the belt. 

Conglomerate is more abundant in the northern part of 
the belt, judging from the description of the Applegate 
group by Wells, Hotz, and Cater (1949, p. 3). The peb- 
bles of the conglomerate are principally subangular frag- 
ments of gray or black chert. A few pebbles are fine- 
grained mica schist. Conglomerate, however, is not men- 
tioned in the description of the Seiad quadrangle (Rv- 
nearson and Smith, 1940), nor in Preston Peak quadrangle 
(fig. 2) (Maxson, 1933). 

Chert is the second most abundant sedimentary rock of 
the belt, but in some broad areas, particularly in the east- 
ern part of the belt, it appears even more abundant than 
slate. It is gray, green, or red, and most commonly forms 
beds about an inch thick that are interbedded rhythmi- 
cally with thinner beds of slate. At many places the inter- 
beds of slate are so thin as to be merely slaty partings, 
which may be so indistinct that the interlayers in sec- 
tions of chert many feet thick can be distinguished only 
by close examination. Much of the chert is recrvstallized, 
and has been referred to by some as quartzite. Cox (oral 
communication, 1956) states that the chert in the Helena 
quadrangle is completely recrvstallized and consists 
wholly of microcrystalline quartz and mica. Fossil radio- 
laria are locally abundant in some of the chert. 

The individual sections of rhythmically bedded chert 
most commonly range from a few feet to several tens of 
feet in thickness; a few, as in the central part of the 
Sawyers Bar quadrangle (fig. 2), appear to be several 
hundred feet thick. One of the thicker sections of chert 
is exposed along the Salmon River for about 10 miles 
west of Cecilville. In this area, Hershey ( 1906, p. 60) 
estimated the chert section to be 3,000 feet thick, but his 
estimate doubtless includes considerable interlavered 



I960 



Northern Coasi Ranges \m> Klamath \1oi\ivi\s 



23 



slate and possibly volcanic rock. Uncommonh chick sec- 
tions of chert associated with volcanic rocks and slate 
are also exposed along the North Fork of Salmon River 
for a distance of lo miles northeast of Forks o( Salmon. 
On the west slope of Orleans Mountain, the thin-bedded 
chert forms sections ranging from SO feet to several hun- 
dred feet in thickness (Hershey, 1906, p. 59). In the 
Helena quadrangle, the Lower Slate series between the 
I ast Fork and the North Fork of the Trinity River is 
unusual!) uniform in width of outcrop and structure. 
I here, Cox (oral communication. 1956) estimates that 
the thin-bedded chert constitutes approximatel) so per- 
cent of a total section that is 2,000 to 4.000 feet thick. 
According to Hinds I 1932, p. 592) chert is most abun- 
dant in the lower parr of the Chanchelulla Peak section, 
but continues as an important element in the upper part. 

Limestone has been found at main scattered localities 
throughout the western heir. It occurs most commonly as 
lenses that range from a tew feet to several hundred feet 
in thickness, hut thicknesses as great as 1,000 feet are 
reported. Dining reconnaissance, no attempt was made to 
trace the limestone hodies along their strike, hut they 
generally seem highly discontinuous and even main of 
the thicker bodies probably arc less than a mile long. 

The limestone bodies of the southern half of the belt 
were described by Diller ( 1905a) as occurring discontin- 
uously along two well-defined parallel zones. I he western 
zone, the so-called southwestern Devonian belt of Diller 
i 1903a, p. 344), is generally within a mile or two of the 
western boundary of the western Paleozoic and Triassic 
belt, and can be traced about 60 miles from near the west 
side of the Sacramento Valley to near the west side of 
1 loopa Valley. The eastern /one, the so-called south- 
western Carboniferous belt of Diller (1903a, p. 348), is 
about in the middle of the western Paleozoic and Triassic 
belt near the Sacramento Valley and from there it trends 
northwesterly "... to the Hall City mines and beyond 
by the base of Chanchelulla to Flay Fork and Bridge 
Creek, where one of the lenses forms a remarkable na- 
tural bridge. From Hayfork Valley the limestones extend 
up Baker ami Big Creeks and were not seen again until 
New River was reached near Patterson"s Ranch" (Diller, 
1905a. (i. $48). 

Diller's (1903a) description of the distribution of the 
limestone seems somewhat oversimplified; during the 
present reconnaissance additional bodies of limestone 
were found, and although some of them occur along the 
general /ones described by Diller, others are between the 
two zones and are of unknown affiliation. The anomalous 
limestone bodies, however, ma) result from local struc- 
tural complexities, and in the southern part do not neces- 
sarilv invalidate Diller's concept of the general distribu- 
tion of the limestone bodies with regard to age. 

In the northern part of the area described by Diller 
(1903a). however, three rather than two zones of lime- 
stone bodies are present. The third is cast of the two 
described by Diller, and only a few miles west of the 
central metamorphic belt. It begins near Junction City in 



the Helena quadrangle and trends ninth to the Salmon 
River about 5 miles west of Cecilville, a distance of more 
than 20 miles. 

Limestone crops our at localities north of the area of 
the three zones just described, but the relation of the 
limestone at these localities with either the so-called 
southwestern Devonian belt or southwestern Carbonif- 
erous belt has not been established. In the Saw vers Bar 
30-minute quadrangle, limestone occurs at several locali- 
ties north of the latitude of Cecilville. farther north, 
limestone has been reported at the Buzzard Hill mine 
and on the ridge between the Buzzard Hill mine and 
Titus Creek in the Ukonom Lake quadrangle (tig. 2). 
Other bodies of limestone have been found in the Dillon 
Mountain and Happy Camp quadrangles. 

In the northeastern part of the Seiad 30-minute quad- 
rangle, limestone has been described by Rynearson and 
Smith (1940. p. 285) as coarse-grained, grayish-white 
marble that forms lenses and layers, in some places nearly 
l.ooo feet thick; and on the west side of Orider Creek 
the marble forms cliffs more than 500 feet high. 

The limestone on the w est side of Grider Creek trends 
southward toward an unusually large and well exposed 
area of limestone in the Marble .Mountains, but has not 
been traced over a gap of nearly 10 miles. Lhe limestone 
on Grider Creek is massive and coarsely crystalline com- 
pared with that of the Marble Mountains area, which is 
relatively thin-bedded and granular, but speculation as 
to their correlation seems warranted because of the 
proximity and similar great thickness. 

In southwestern Oregon the limestone in the western 
Paleozoic and Triassic belt was described by Diller 
(Diller and Kay, 1909, p. 50, 51) as occurring in four 
northeast-trending zones containing about 50 masses, the 
largest outcrop being more than a third of a mile long 
and 200 feet thick. The limestone of the two western 
zones he considered to be of Devonian age; that of the 
two eastern zones he considered to be of probable Car- 
boniferous or Triassic age. In his description of the 
limestone deposits of southwestern Oregon, Diller did not 
mention the so-called southwestern Devonian belt ami 
southwestern Carboniferous belt of the southern Klamath 
Mountains in California, but the similarity of his descrip- 
tions of the two areas regarding the distribution of the 
limestone zones relative to age is notable. 

Volcanic rocks of the western belt range in compo- 
sition from andesitic to basaltic ami generally they are 
so altered to greenstone that original textures and struc- 
tures arc destroyed. At some localities, vesicles, pillow- 
structure, and agglomerate structure are seen in some 
of the greenstone, and these rocks are considered to be 
extrusive. Some of the greenstone appears to be in- 
trusive, and some is interbedded with the slate, chert 
and limestone. The relation of much of the greenstone 
to the other rocks was not determined, however, and 
some of it may be equivalent to the Copley greenstone 
of the eastern Paleozoic belt. 



24 



California Division of Minis 



Bull. 179 



Dillcr (1903a) noted the common association of vol- 
canic rocks and chert with the limestone of both the 
so-called southwestern Devonian and southwestern Car- 
boniferous belts, but did not clearly state that he con- 
sidered the limestone and chert to be interbedded with 
the volcanic rocks. Neither Hershey (1901) nor Hinds 
(1932) considered the volcanic rocks to be interbedded 
with strata of the Lower Slate series or Chanchelulla 
formation, respectively, and Hershey (1906, p. 61) states 
that he saw no volcanic rocks interbedded with the 
Blue Chert series. Cox (oral communication, 1956), how- 
ever, noted flow breccia and pillow lava interbedded 
with the slate and chert in at least three places along the 
road from Helena to Hobo Gulch and at numerous 
other localities in the Helena quadrangle, but he esti- 
mates the volcanic rocks to amount to no more than 5 
percent of the stratigraphic section. 

The extrusive volcanic rocks of the belt were con- 
sidered by Hershey (1901, p. 235) to be correlative with 
the Clear Creek formation, a name he applied to the 
Copley greenstone of Devonian age in the eastern Paleo- 
zoic belt (Hershey, 1901, p. 226, 233). However, he 
thought the Clear Creek formation to be of Mesozoic 
age, and to rest uncomformably on the Lower Slate series 
of Devonian to Carboniferous age (1901, p. 238). Her- 
shey interpreted the greenstone in the Lower Slate series 
to be intrusions related to a so-called Clear Creek (Cop- 
ley) stage of volcanism. Hinds (1932, p. 392) suggests 
a similar explanation for greenstone in the Chanchelulla 
formation, and states that the Chanchelulla formation is 
overlain by the Copley greenstone. 

In the northern part of the western Paleozoic and 
Triassic belt, volcanic rocks have been described as inter- 
bedded with the slate, chert, and limestone. Maxson 
(1933, p. 128) mentions flows of basalt interbedded with 
rocks of so-called Devonian age in the Preston Peak 
quadrangle. In the Seiad quadrangle, the volcanic rocks 
are basaltic and andesitic flows and sills with thin layers 
of sandstone, tuff, and shale, and some thick layers of 
limestone, hut most are altered to schists and gneisses 
(Ryncarson and Smith, 1940, p. 285). In southwestern 
Oregon, the Applegate group is dominantly extrusive 
volcanic rock with many thin but continuous lenses of 
tuffaceous sedimentary rocks, slate, quartzite, and chert, 
and stubby lenses of limestone (Wells, 1955). 

The rocks of some areas along the east side of the 
western Paleozoic and Triassic belt in central and north- 
ern Siskiyou County and southern Oregon are of a 
higher metamorphic grade than is common elsewhere in 
the belt. In southern Oregon, these rocks crop out over 
an area of approximately 40 square miles in the south- 
western part of the Medford quadrangle. They have 
been referred to as so-called younger metamorphic rocks 
by Wells and others (1939) and described as ". . . chiefly 
quartzites, quartz-mica schist, and quartz-amphibole 
schist, with lesser amounts of amphibolite and argillite 
and thin bands of marble. . . . They were probably de- 
rived for the most part from quartzose sediments with 



small interbeds of shale and limestone. The amphibolites 
were probably formed by metamorphosis of basic igne- 
ous rocks." The rocks were first considered to be older 
than the adjacent Applegate group of Triassic (?) age, 
but more recently they are thought to be a metamorphic 
facies of the Applegate group (Wells, Hotz, and Cater, 
1949, p. 3, and Wells, 1955). 

In northwestern California, somewhat similar rocks 
were seen during the present reconnaissance in the Marble 
/Mountains area, and along the Scott River between Scott 
Valley and the mouth of Kelsey Creek. In the northern 
part of the Yreka 30-minute quadrangle (rig. 2), par- 
ticularly along the Klamath River, the rocks of certain 
areas have been described (Averill, 1931, p. 9) as in- 
cluding "... a great variety of metamorphic material, 
argillites, phyllites, quartzitic slates, very fine grained 
black schists, quartzites, talcose schists, pyroxene-horn- 
blende schists, limestone and marble." The general area 
of distribution of these metamorphic rocks is roughly 
contiguous with areas of the so-called younger meta- 
morphic rocks or metamorphosed Applegate group of 
southern Oregon, and perhaps the rocks of these areas 
are equivalent. 

In the Marble Mountains the rocks consist chiefly of 
thin-bedded amphibolite and chlorite schists, quartzite, 
and marble, and they appear to constitute a section that 
is more than 10,000 feet thick (W. P. Pratt, written com- 
munication, 1957). The marble is thin bedded and granu- 
lar, and is exposed for much of a distance of 5 miles 
along the north-trending ridge of the Marble Moun- 
tains. The strata along the ridge generally dip eastward 
at low angles, and along the southern part of the ridge 
the marble forms a dip-slope exposure more than a mile 
wide. The west face of the Marble Mountains is steep, 
and from a distance the strata that underlie the marble 
appear to be well exposed (photo 2). 

The total thickness of the sedimentary and volcanic 
strata deposited in the western Paleozoic and Triassic 
belt is not known. Estimates of thickness of the Lower 
Slate series, Blue Chert series, Chanchelulla formation, 
and Copley (?) greenstone have been made by others 
at several widely spaced localities, but owing to con- 
flicting references regarding order of superposition, cor- 
relation, and ages of the rocks, it is not feasible to add 
the individual estimates to arrive at a total thickness. 

Hershey (1901, p. 233) states ". . . the thickness of 
the [Lower Slate] series in any one section is not known 
to me. L T sually the succession of strata is repeated sev- 
eral times in a single area by faulting and folding . . . 
and an estimated average for the entire territory of 5,000 
feet probably is sufficiently accurate for the present." 
Hershey, (1906, p. 60) estimated the Blue Chert series 
to be 5,000 feet thick in the central part of the Sawyers 
Bar quadrangle. The Chanchelulla formation exceeds 
5,000 feet in thickness, and the additional thickness caused 
by abundant concordant bodies of greenstone, attributed 
by Hinds to intrusion of Copley greenstone, may be con- 
siderable, as some of the greenstone bodies are 500 feet 
thick (Hinds, 1932, p. 392). 



19601 



Northern Coasi Ranges \m> Kiwium \1oi\ivi\s 



25 




Photo -. Aerial view, looking cast coward the southern p.irr of tin Marble Mountains. I he light-colored outcrops along the 
crest of the ridge arc marble. A small part of the Scott Valley can be seen in the middle distance. Peaks of volcanic rocks oi the 
Cascade Range province, including Mount Shasta (wreathed in clouds), arc along the horizon. Photo GS-OAD, 1-101, September 
I9S3. 



The volcanic rocks (Copley? greenstone) exposed 
along Pearch Creek near Orleans, intrude and uncon- 
formably overlie the Blue Chert series, and are estimated 
to be 800 to 1,200 feet thick (Hershey, 1906, p. 60). The 
Cople\ ( : ) greenstone intrudes and unconformabl) oxer- 
lies the Chanchelulla formation, and two incomplete sec- 
tions measured in the Weaverville quadrangle arc 1,200 
and 1,500 feet thick (Hinds, 1932, p. 394). The thickness 
of the volcanic section in the south-central part of the 
western Paleozoic and Triassic belt is not known. 

Age of the Rocks. Few paleontologic data are avail- 
able for assigning an age to the rocks of the western 
Paleozoic and Triassic belt. Fossils have been found only 
in the limestones, with the exception of radiolaria in 
some of the cherts. Generally the fossils are poorly pre- 
served, as most of the limestone is coarsely recrystallized. 

Dillcr ( 1903a) divided the rocks of the southern part 
of the western Paleozoic and Triassic belt into so-called 
southwestern Devonian and southwestern Carboniferous 
belts. The age assignments were based on fossils collected 
from limestone bodies at widely spaced intervals along 
the belts. In southwestern Oregon, Dillcr (Dillcr and 



Kay, 1909) described the limestone bodies of the western 
Paleozoic and Triassic belt as occurring in four parallel 
northeast-trending zones. Fossils identified as Devonian 
in age were found in the limestone of the two western 
zones, but only crinoid stems of indeterminate age were 
fount! in the two eastern /ones. The general absence of 
fossils other than crinoid stems in the two eastern /ones 
suggested to Dillcr an .v^i: different from Devonian, and 
he considered the limestone bodies likely to be Car- 
boniferous or Triassic in age. 

Partial re-examination of Diller's collection of fossils, 
in addition to a few newer discoveries of fossils, shows 
that at least some, and perhaps most, of Diller's age 
assignments of the limestones of the western Paleozoic 
and Triassic belt are in error. The limestone of the so- 
called southwestern Carboniferous belt seems to be 
Permian and perhaps Late Pennsylvanian in age and the 
limestone of at least one locality in the so-called south- 
western Devonian belt is Triassic in age. 

Diller's collection of fossils from his locality no. 705 
(Oilier, 1903a. p. 344-345), sec. 30, T. 2S N., R. 10 W., 
near the south end of his so-called southwestern Devonian 



26 



California Division of Mines 



Bull. 179 



belt, were re-examined by N. J. Silberling of the U.S. 
Geological Survey. According to Silberling (written 
communication, 1958): 

"These fossils were considered Devonian in age by Diller 
[1903a] (Am. Jour. Sci., 4th ser., v. 15, p. 345) who quotes Schu- 
chcrt as having recognized 'two species of Ammonoids of the 
family Prolecamtidae 1 in the collection. Accompanying the col- 
lection is an undated note signed by J. M. Clarke which reads 
'Posidonia and [a] Goniatite— like Gastrioceras— [these] indicate 
Carbonic age and probably Coal Aleasures . . .' A more recent 
label (possibly prepared by A. K. Miller) reads 'Proarcests sp. 
etc. . . . Upper Triassic. . . .' 

"Several of the small fragmentary ammonites can be assigned 
to the genus Arcestes, sensn lato. These specimens have smooth 
involute globose shells with periodic constrictions of the whorls. 
In addition one of the specimens with these characters shows 
part of the suture which has numerous complexly crenulated 
elements. A more refined identification is not possible because 
the recognition of subgenera within the genus Arcestes depends 
on features of the body chamber and this part of the shell is not 
preserved. 

"Also present are three fragmentary impressions representing 
a coiled shell with finely-spaced strigate ornamentation. These 
are suggestive of the Upper Triassic ammonite genus Cladiscites. 

"The age of this collection is .Middle or Late Triassic, prob- 
ably Late Triassic." 

An ammonite collected from limestone in the so-called 
southwestern Carboniferous belt, in sec. 30, T. 30 N., R. 
10 W., near Wildwood, was identified by J. P. Smith 
(Diller, 1903a. p. 350) as Permian in age. It has been re- 
examined and is thought to be Middle or Late Permian 
in age (Miller, Furnish, and Clark, 1957, p. 1062-1063). 
Each limestone body seen during the present recon- 
naissance was searched briefly for fossils, and although 
poorly preserved crinoid stems were seen in many of 
these, diagnostic fossils were found at only two localities. 
Abundant microfossils were collected by Cox at Hall 
City Caves (locality no. 17, p. 1) in SE'4 sec. 32, T. 30 
N., R. 10 W., in the northeastern part of the Hoaglin 
quadrangle. The locality probably is the same as Diller's 
(1903a, p. 349) Hall City locality no. 702, and doubtless 
is part of the so-called southwestern Carboniferous belt. 
The fossils w ere examined by L. G. Henbest of the U. S. 
Geological Survey, who reports (written communication, 
June 29, 1956) the following: 

"The foraminifers in this sample consist of two or more species 
of Climacammina, primitive Miliolidae (?), a species of fusulin- 
ellid, and apparently two species that belong to Staffella, Ozaivai- 
nella, or possibly Eoverbeekina. Within certain limits, the strati- 
graphic range of each of the above listed genera in the Pacific 
and Asian realms is problematic. Poor preservation prevents a 
close determination of the fusulinids. The assemblage is not older 
than Middle Pennsylvanian nor younger than the middle part 
of the Permian. Permian rather than Pennsylvanian age seems 
most likely, but the evidence is vague." 

Fossiliferous limestone float was found by the writer 
near the center of the mutual boundary between the 
Hayfork and Weaverville 15-minute quadrangles (lo- 
cality no. IS, pi. 1). The locality is in center sec. 21, T. 
32 N., R. 10 W., on a logging trail on the north side of a 
creek, and about 200 feet west of a sharp bend in the 
Douglas City-Hayfork road. The limestone seems to be 
broadly assignable to Diller's so-called southwestern Car- 
boniferous belt, although it is several miles east of the 



trace of the limestone bodies he used to define the belt, 
and only a mile west of the central metamorphic belt. 
The limestone was examined by L. G. Henbest, who re- 
ports (written communication, April 14, 1958) as fol- 
lows: 

"This altered limestone contains a considerable abundance of 
fusulinids. In the rock slices submitted, it was possible to recog- 
nize that most of the specimens belong to a peculiar species of 
Triticites whose features suggest early as well as late stages in 
the evolution of the genus. A few specimens even suggested a 
transitional stage into Pseudofusulina. A few of the fusulinids, 
seen only in odd sections, have some resemblance to Dmibari- 
nella. Two fragmentary specimens resembling the juvenarium of 
Schubertella or the microspheric generation of a larger fusulinid 
were also recognizable. Late Pennsylvanian or McCloud Permian, 
age seems to be as close a determination as can be made on the 
material at hand." 

Wells, Hotz, and Cater (1949, p. 3, 4) consider all of 
the rocks of the western Paleozoic and Triassic belt in 
southwestern Oregon to be of Triassic(P) age, because 
". . . Reeside studied the collections of fossils made by 
the writer and re-examined the collections made by 
Diller. He pronounced them to be of Mesozoic age, 
probably Late Triassic." 

Formations of Jurassic and Cretaceous Ages 

The rocks of Jurassic and Cretaceous ases in the north- 
ern Coast Ranges and Klamath Mountains are subdivided 
into several formations that consist mainly of interbedded 
grayw acke and shale, but a few of these formations con- 
tain considerable thin-bedded chert and volcanic rocks. 
The ages of most of the formations are poorly known, 
as few diagnostic fossils have been found, and as some 
of the paleontologic data are not compatible with ap- 
parent structural relations. Formational designation has in 
some cases been based largely on geographic distribution, 
and many conflicting formational designations and strati- 
graphic interpretations have been made owing to the 
general similarity of the rocks and the scarcity of fossils, 
as well as to the structural disarrangement and generally 
poor exposures. Along the west side of the Sacramento 
Valley, however, the strata form an orderly sequence 
from Upper Jurassic to Upper Cretaceous. 

The formations are most conveniently discussed under 
three major headings; rocks of middle Late Jurassic age, 
rocks of late Late Jurassic and Cretaceous age, and rocks 
of late Late Cretaceous age. The rocks of middle Late 
Jurassic age form the westernmost belt of the Klamath 
.Mountains arc, and appear to have been deformed, lo- 
cally metamorphosed, and intruded by granitic rocks 
prior to deposition of the rocks of late Late Jurassic and 
younger ages. 

The rocks of late Late Jurassic and Cretaceous ages 
are the principal formations in the northern Coast Ranges 
of California and along the west side of the Sacramento 
Valley. A few relatively small patches of some of these 
formations lie with high angular unconformity on the 
rocks of the Klamath Mountains arc. In southwestern 
Oregon large areas of rocks of late Late Jurassic and 
Cretaceous ages have been included in the western part 



I will 



Northern Coasi Ranges \m> Kiwiuii Moisiuns 



27 



of the Klamath Mountains province as rlic outline <>t the 
province was drawn 1>> Diller I 1902, pi. 1 ). 

The rocks discussed as hue Late Cretaceous in age 
maj in fact range into early Tertiary. They probably 
were deposited \\ irh marked disconformitj on the rocks 
of early Late Cretaceous and older ages. In northwestern 
California they occur chiefly at three localities in the 
Coast Ranges. The largest area is in western Humboldt 
County. ;i second area is immediatel) west ol the San 
Vndreas fault in northwestern Sonoma and southwestern 
Mendocino Counties, and a third is near Covelo in north- 
central Mendocino County. 

Rocks of Middle Late Jurassic Age, Klamath Mountains 

I he Galice and Dothan formations are the oldest 
known Jurassic rocks in northwestern California and 
southwestern Oregon. The Galice formation previouslj 
had been mapped in southwestern Oregon and in north- 
ern Del Norte County, California. During the present 
reconnaissance, rocks thought to be of the Galice for- 
mation were traced southeastward along the western part 
of the Klamath Mountains province from Del Norte 
County, through northeastern I [umboldt County, to 
west-central Trinity County. Near Weitchpec in north- 
eastern Humboldt County, the rocks thought to he of 
the Galice formation appear to grade westward into 
schist. The schist forms a narrow heir along most of the 
western boundan of the Klamath Mountains province 
in California and is known variously at several different 
localities along the belt as the South Fork Mountain belt 
of Diller | 1903a), Weitchpec schist of Hershey I 1906), 
and Kerr Ranch schist of Manning and Ogle (1950). It 
generally has been considered to correlate with the Ab- 
rams formation of the central mctamorphic belt of the 
Klamath Mountains arc. and to be pre-Silurian or older 
in age, but in this report it is considered to be chiefly 
a mctamorphic facies of the Galice formation of middle 
Late Jurassic age. 

The Dothan formation has been studied mostly in 
southwestern Oregon. The only area of significant size 
in California that consists of rocks considered by some 
geologists to belong to the Dothan formation is an area 
chiefly ot graywacke and shale just west of the Klamath 
Mountains province in western Del Norte and northern 
1 [umboldt Counties. The rocks of the same area are con- 
sidered b) the waiter and others to be part of the Fran- 
ciscan formation, although the Dothan and Franciscan 
genera Ih are not considered correlative. 

The age of the Galice formation is middle Late Jur- 
assic on the basis of paleontologic evidence, but the 
relative age of the Dothan formation, whether older or 
younger, has been in dispute since the two formations 
were named by Diller (1907). The Dothan is thought 
to grade upward into the Galice formation by Taliaferro 
( 1942, p. 83), and Cater and Wells (1954, p. 85). 

Galice Formation. The Galice formation is the name 
applied b\ Diller (1907, p. 403) to slaty, dark to black, 
fine-grained sediments and subordinate sandstone and 
conglomerate exposed along Galice Creek in south- 



western Oregon. Wells. Mot/, and Cater (1949. p. 4) 
redefined the Galice formation to include a considerable 
quantity of intercalated volcanic rock. In northwestern 
California the Galice formation has been mapped in the 
northwestern parr of the Preston Peak 15-minute quad- 
rangle (Maxson, 1933, p. 129-130) and in the Gasquet 
quadrangle (fig. 2) (Cater and Wells. 1954, p. SY>- n 2>. 
In rhc adjacent parr of Oregon it crops out continuously 
for about so miles in a northeast-trending band along the 
west side of the western Paleozoic and Triassic belt. 

In the Gasquet quadrangle, the Galice formation has 
been described as consisting of a lower metavolcanic- 
rich section and an upper metasedimentary section (Cater 
and Wells, 1954, p. 86). The most abundant metavol- 
canic rocks are greenish meta-andesite flows and flow- 
breccias. Others include nierabasalf, spilite. metarhyo- 
lite(r), meta-andesite tuff, metarhyolite tuff and agglom- 
erate. A few lenses of black slate are intercalated with 
the volcanic rocks. The thickness of the metavolcanic- 
rich section is thought to be at least 7,000 feet, but in 
Oregon thicknesses of 10,000 and 15,000 feet have been 
estimated in the Kerby ami Galice quadrangles, respec- 
tively (Wells, Hot/, ami Cater. 1949, p. 7; and as the 
Rogue formation in Wells and Walker. 1953). 

The overlying section of metasedimentary rocks con- 
sists principally of slaty and ph) llitic shales w ith inter- 
bedded tuffaceous sandstones. Cater and Wells (1954, 
p. 91-92) found one small lens of gray marbleized lime- 
stone interbedded with slate and sandstone in the Gasquet 
quadrangle. Chert has not been reported in the literature 
as a constituent of the Calice formation, bur an excellent 
exposure of rhythmically thin-bedded chert was seen in 
the Galice formation in the northwestern parr of the 
Preston Peak 15-minute quadrangle during the present 
reconnaissance. 

The sandstones of the Galice formation are graywacke, 
generally tine to medium grained, and range from gray 
to green where unweathered, The) consist principalis 
of angular grains of plagioclase, quartz, augite, horn- 
blende, chlorite, epidote, micas, fragments of volcanic 
rocks, quartzite, and shale, shards of devitrificd glass, and 
minor amounts of carbonaceous and argillaceous ma- 
terial (Cater and Wells, 1954, p. 91 ). Graded bedding 
is present at some places. The graywacke is megascopic- 
ally similar to that of other formations of Jurassic and 
Cretaceous ages that are widely distributed throughout 
northwestern California and southwestern Oregon. 

The thickness of rhc metasedimentary section of the 
Galice formation has been estimated to be at least 3,000 
feet (Cater and Wells, 1954, p. 84) in the Gasquet quad- 
rangle. Wells, Hotz, and Cater (1949, p. 7) estimate a 
thickness of at least 15,000 feet in the Kerby quadrangle, 
Oregon. In rhc Riddle quadrangle, Oregon, the thick- 
ness was estimated to be between 1,000 and 2,000 feet 
l.\ Diller (Diller and Kay, 1924, p. 2). 

The Galice formation is middle Late Jurassic in age, 
based on paleontologic evidence, and may be correlative 
with the Mariposa slate of the Sierra Nevada (Diller, 



28 



California Division or Minis 



I Bull. 179 



1907, p. 404-405; Taliaferro, 1942. p. 77; and Cater and 
Wells, 1954, p. 92). The age and correlation is based 
principally on the occurrence of Bnchia erringtoni 
(Gabb) \ a species whose range in age, according to 
R. \Y. Imlay (written communication, Nov. 26, 1958), 
is late Oxfordian to middle Kimmeridgian, and which 
has been found also in the Mariposa slates. 

Slaty and phyllitic shales and sandstones throughout 
a large area in western Siskiyou, northeastern Humboldt. 
and western Trinity Counties appear to be a southeast- 
erly continuation of the rocks described as the Galice 
formation in northern Del Norte County, but they have 
a slightly higher metamorphic grade. They occur along 
the east side of the narrow belt of schist that forms most 
of the western boundary of the Klamath .Mountains in 
California, and are bounded to the east by plutonic rocks 
and the western Paleozoic and Triassic belt. 

The rocks are shales, sandstones, and minor conglom- 
erates, but are mostly converted to slate and phyllite. 
They have not been studied in thin section, but where 
the original character of the rocks has not been masked 
by metamorphism, the sandstones appear to be gray- 
wacke. 

Cleavage is well developed at most exposures, and 
generally is nearly parallel to the bedding. The strata 
are folded gently to moderately throughout most of the 
area, and dip most commonly to the northeast. Steep 
dips, however, are not rare. 

The thickness of the slate and phyllite appears to be at 
least several thousand feet, based on the topographic re- 
lief of areas uniformly underlain by these rocks. In the 
northeastern part of the Willow Creek quadrangle 
(fig. 2), the topographic relief between the Trinity River 
and Waterman Ridge several miles northeast is about 
2,500 feet, and owing to the general northeast dip of the 
rocks it seems likely that the phyllite is considerably 
thicker. On the east side of Hoopa Valley, a logging road 
climbs the ridge along the north side of Hostler Creek 
to the Ironside Mountain batholith (pi. 1), a distance of 
about 5 miles across the strike of the phyllite and an 
altitude of 3,200 feet above the valley. The strata crossed 
by the road dip at an average of perhaps 25 degrees 
northwestward. They appear to constitute a stratigraphic 
section that is at least 10,000 feet thick unless 'serious 
error in measurement has been introduced by faulting 
or folding. Neither the top nor the bottom of the sec- 
tion has been recognized. 

Greenstone was found interlavered with the weakly 
metamorphosed sediments at only a few places. Phyllitic 
pyroclastic(r) rocks crop out in places along the road 
between Weitchpec and Orleans; near Red Cap Gulch, 
along the same road, some of the greenstone shows pillow 
structure. 

The Galice formation may be more widespread than 
is indicated on the geologic map (pi. 1), as some areas 
of volcanic rock, perhaps equivalent to the volcanic rocks 

1 The name Buchia is used throughout this report instead of the 
synonym Aucella, except for quotations. 



of the Galice formation in Del Norte Count), may have 
been mapped as part of the western Paleozoic and Tri- 
assic belt in northeastern Humboldt and southwestern 
Trinity Counties. The outlines of the Galice formation 
shown on the geologic map were drawn chiefly on the 
basis of an abrupt change in the widespread, fairly uni- 
form tcrrane of slaty and phyllitic sandstones and shales. 
It is unlikely that relatively small areas of slates and 
phyllites, and possibly greenstones, of the Galice for- 
mation would have been distinguished from somewhat 
similar rocks of the western Paleozoic and Triassic belt 
during the present reconnaissance. 

The slaty and phyllitic shales and sandstones of north- 
eastern Humboldt and southwestern Trinity Counties are 
thought to be a southeasterly continuation of the Galice 
formation of northern Del Norte County. The correla- 
tion, however, is based only on lithology and geographic 
continuity, as no fossils were found. The shales and 
sandstones of the Galice formation in northern Del Norte 
County generally are slaty rather than phyllitic. In the 
northern part of the Orleans quadrangle, as one travels 
southward along the ridge that forms the boundary be- 
tween Del Norte and Siskiyou Counties, the slaty rocks 
appear to grade through a distance of several miles into 
the phyllitic rocks of the so-called Galice formation of 
Trinity County. 

Determination as to whether the slaty and phyllitic 
shales and sandstone in northeastern Humboldt and 
southwestern Trinity Counties are actually the Galice 
formation, or perhaps the Bragdon formation of pre- 
Jurassic age must await further study. They were first 
described by Hershey (1904, p. 349-354) as a western 
area of the Bragdon formation, and compared with the 
nonmetamorphosed Bragdon formation of the type area 
in the eastern Paleozoic belt. He considered the Bragdon 
formation to be Jurassic in age (Hershey, 1901 and 
1904), principally owing to the lithologic similarity of 
the rocks of the so-called western area of the Bragdon 
formation to the Mariposa slate of the Sierra Nevada. 
Oilier (1903a and 1905), however, showed the Bragdon 
formation of the type area in the eastern Paleozoic belt to 
be largely Mississippian in age, an age Hershey (1906) 
was reluctant to accept. It is likely that Hershey later 
considered the rocks of the so-called western areas of the 
Bragdon formation to be equivalent to the Galice for- 
mation, as in 1911 he published a reconnaissance map of 
Del Norte and western Siskiyou Counties on which he 
shows a band of the Galice formation trending south- 
eastward across the northern boundary of Humboldt 
County. The band is in line and contiguous with areas 
of phyllite he previously described as western areas of 
the Bragdon formation. 

South Fork Mountain Belt of Diller, Weitchpec Schist 
of Hershey, and Kerr Ranch Schist of Manning and 
Ogle. Schists form a narrow selvage along nearlv the 
entire 1 50 mile length of the southern and western boun- 
dary of the Klamath .Mountains province in California, 
and occur also in two subparallel bands to the west in 



I960 I 



Nokiiiikn Cium Ranges \m> Kivmmii \lm\ni\s 



29 



the Coast Ranges area of northern Humboldi County. 
Diller (1903a, p. $43) referred to these schists synony- 
mous!) as the southwestern belt <>t schists and the South 
Fork Mountain belt of schists. They were named 
Weitchpec schist by Hershey ( 1906. p. 63; also see 1904. 
p. 357) for exposures near the settlement of Weitchpec 
at the confluence of the Trinity and Klamath Rivers in 
the northwestern part of the Hoopa quadrangle (fig. 2). 
Most recently they have been referred to ;is the Ken- 
Ranch schist for exposures near Kerr Ranch in the 
southwestern part of the Blue Lake quadrangle (tiy. 2) 
(.Manning and Ogle, 1950, p. 13). In Del Norte County, 
the schist has been described by Maxson (1933, p. 128) 
and Rice (1953, p. 2779). In southwestern Oregon, 
seemingly related rocks were named Colebrooke schist 
by Diller (1903b, p. 2). For convenience in further dis- 
cussion, the name South Fork .Mountain schist will be 
used in reference to the above-mentioned schists in 
California. 

The South Fork .Mountain schist underlies a continu- 
ous, even-crested ridge that marks the southern and most 
of the western boundary of the Klamath Mountains 
province in California. At the southern boundary of the 
Klamath Mountains province the ridge trends N. 70 W. 
for 30 miles, the higher points along the ridge being 
North Yolla Boll) and Black- Rock Mountains. The 
southwestern boundary of the province is the South Fork 
Mountains which trend V JO W. for about 50 miles 
along the west side of the South Fork of the Trinity 
River. The crest and northeast slope of the South Fork 
Mountains are underlain by schist. The southwestern 
slope is an area of abundant landslide and poor exposure, 
and small areas cither of schist or of graywacke of the 
Franciscan formation are found at short distances below 
the crest of the ridge and on the middle slopes. 

Near the north end of the South Fork Mountains, an 
en echelon ridge to the west. Redwood Mountain, begins 
and trends \. 25 W. for 4o miles at decreasing altitudes 
to the coast. The crest of this ridge also is schist, whereas 
the lower slopes arc dominantly rocks of the Franciscan 
formation. 

From the north end of the South Fork Mountains, the 
continuation of the province boundary ridge is some- 
what more irregular anil trends northward approximately 
30 miles to near Weitchpec. where the Klamath River 
has cut a deep notch across the belt of schist. North of 
the Klamath River the schist continues a few miles along 
the western face of the ridge, the crest being underlain 
along most of the succeeding 40 miles to the southwest- 
ern part of the Gasquet quadrangle, by serpenrinized 
ultramafic rock. In the northern part of the Tectah Creek 
quadrangle (fig. 2). and northward, the rocks in the 
narrow belt along the west side of the ultramafic rocks 
are in general phyllitic or slaty, rather than schistose, and 
these rocks possibly belong to the Franciscan formation 
to the west rather than belonging to the South Fork 
Mountain schist. 



The schist consists dominantly ol quartz and sericite, 
but in some areas greenschist containing chlorite or 
epidote is abundant. According to Manning and Ogle 
(1950, p. L3) the Kerr Ranch schist includes metacon- 
glomerates, metacherts. and glaucophanc schists. During 
the present reconnaissance the diverse rock types in- 
cluded by Manning and Ogle were not seen, and it may 
be that they are most common to the Redwood Moun- 
tain belt. 

I he quartz-sericite schist is thinly foliated and gen- 
erally dark-gray. The folia consist principally of alter- 
nate layers of sericite and an aggregate of quartz and 
plagioclase. Most of the schist is crenulated, and the amp- 
litude of the crenulations commonly ranges from % to '/ 2 
inch. Locally the schist is more highly deformed and 
contains abundant small lenses and irregular masses of 
quartz. 

The age and formational affiliation of the South Fork 
.Mountain schist is not entirely clear, but generally the 
schist has been considered to be pre-Devonian or perhaps 
Precambrian in age, and genetically unrelated to adjacent 
formations. The South Fork Mountain schist has most 
commonly been correlated with the Abrams formation 
of the central metamorphic belt of the Klamath .Moun- 
tains arc. However, more than one adjacent formation 
is at least in parr a lithologically suitable prototype for 
the schist, and one of these, the Galice formation, appears 
to grade into the schist near Weitchpec. The schist max 
represent a narrow zone of dynamic metamorphism, and 
although the metamorphism may have transgressed for- 
mational boundaries, most if not all of the schist is likely 
a metamorphic equivalent of the slaty and phyllitic rocks 
herein correlated with the Galice formation of middle 
Late Jurassic age. 

The contact between the Weitchpec schist and the 
slaty and phyllitic sandstones and shales of the Galice 
formation is generally abrupt, and at most places is prob- 
ably a fault. However, at a few places the slaty and 
phyllitic rocks of the Galice formation can be seen to 
grade into the Weitchpec schist. This gradation is best 
seen along the Klamath River near Weitchpec and along 
the Trinity River between Weitchpec and Hoopa Val- 
ley, where it was described by Hershey ( 1906, p. 63). 

On the west slope of the South Fork Mountains and 
northward to near Weitchpec, the schist is in contact 
with nonmetamorphic rocks of the Franciscan formation 
a short distance below the crest of the ridge. The contact 
relation is obscure, but owing to the uniform outline of 
the belt, to abundant landslides, and to the lack of grada- 
tional rocks, the contact appears likely to be a high-angle 
fault. 

The schist along Redwood Mountain appears similar 
to that of .the South Fork .Mountains, bur in general the 
schistosity is not as well developed and lenses of quartz 
are less abundant. The two belts are separated by a cor- 
ridor of nonmetamorphosed sandstones and shales of the 
Franciscan formation that narroxvs southeastw ard to ap- 
proximate! v a mile in width near the southeast end of the 



30 



California Division of Mines 



Bull. 179 



Redwood Mountain belt. The contacts along both sides 
of the Redwood Mountain belt of schist appear to be 
thrust faults that dip northeast (Manning and Ogle, 1950, 
p. 2"; Rice, 1953, p. 2779). The schist in the small area 
west of the Redwood Mountain belt and near Trinidad 
Head is poorly exposed, but it is considered by S. J. Rice 
(oral communication, 1955) to be a remnant of a block 
that was thrust over rocks of the Franciscan formation. 

Although Hershey ( 1906, p. 63 ) recognized the grada- 
tional relation between the schist and the phyllitic sand- 
stones and shales adjacent to the east near YVeitchpec, he 
nevertheless stated that "... undoubted pre-Devonian 
schists occur in South Fork Mountain." He probably 
was reiving on reconnaissance observations by Oilier, 
who stated in connection with a description of the Cole- 
brooke schist of southwestern Oregon, that "... on 
South Fork of Trinity River a mica schist, probably of 
the same age as the Colebrooke schist, is overlain by 
strata containing Devonian fossils" ( Oilier, 1903b, p. 2). 
During the present reconnaissance this relation was not 
seen. 

Rocks of late Late Jurassic and Cretaceous age are not 
known to be in depositional contact with the South Fork 
Mountain schist in California. In southwestern Oregon, 
however, the younger Mesozoic rocks are in depositional 
contact with the Colebrooke schist, and as the Cole- 
brooke schist is considered correlative with the South 
Fork Mountain schist, a means is provided for closely 
dating the metamorphism of the Galice formation. 

The Colebrooke schist occurs in the Port Orford quad- 
rangle, southwestern Oregon, principally in two large 
areas surrounded mainly by sandstones and shales of the 
Myrtle formation of Oilier that ranges from late Late 
Jurassic to Cretaceous in age. It was described by Diller 
(1903b, p. 2) as sericite schists, phyllites and slates that 
were derived from sedimentary rocks, and he considered 
it equivalent to the schists along the South Fork of the 
Trinity River. On a geologic map of southw estern Ore- 
gon, Wells ( 1955) discarded the name Colebrooke schist, 
and showed those areas of rocks as having been derived 
from the Rogue formation, which consists of lava flows, 
tuff, agglomerate, and Mow breccia, mostly of dacitic 
and andesitic composition, and of Jurassic age. He de- 
scribed the rocks formerly named Colebrooke schist as 
banded crystalline rocks made up of dark hornblende- 
rich layers and light siliceous layers. Cater and Wells 
(1954, p. 86) correlate the Rogue formation with the 
lower, metavolcanic part of the Galice formation. 

The Colebrooke schist is overlain unconformablv by 
the Myrtle formation of Diller. Diller ( 1903b, p. 2) states 
that "... the Myrtle formation surrounds a number of 
small areas of Colebrooke schist, with which it is in con- 
tact, and the basal portion is a conglomerate containing 
many fragments of the schist. The conglomerate com- 
monly contains Aucella crassicollis." This species is 
common in the older part of the Shasta series of Early 
Cretaceous age along the west side of the Sacramento 
Valley. Elsewhere in the Myrtle formation of Diller, 



Buchia piochii (Gabb) of late Late Jurassic (middle 
Tithonian) age occurs, a species common to the Knox- 
ville formation along the west side of the Sacramento 
Valley. Although the strata containing Buchia piochii 
(Gabb) have not been found in depositional contact with 
the Colebrooke schist, it seems reasonable that they too 
were deposited after rnetamorphism of the Galice forma- 
tion of middle Late Jurrasic (late Oxfordian to middle 
Kimmeridgian) age. .Metamorphism of the Galice for- 
mation therefore seems likely to have occurred between 
the middle Kimmeridgian and middle Tithonian stages 
of the late Jurassic. 

Rocks of Late Jurassic and Cretaceous Age 

Formations that range from late Late Jurassic to Late 
Cretaceous in age are the principal rocks of the northern 
Coast Ranges and along the west side of the Sacramento 
Valley, and at some places overlie the rocks of the 
Klamath .Mountains arc. The formations consist chiefly 
of graywacke and shale, with exception of the Franciscan 
formation of the Coast Ranges which also includes con- 
siderable interbedded chert and volcanic rocks. 

The graywacke and shale along the west side of the 
Sacramento Valley are well exposed in a north-trending 
belt (photos 3 and 4), and locally contain abundant 
fossils. They form an essentially conformable sequence 
of strata that are subdivided into the Knoxville formation 
of late Late Jurassic (middle Tithonian) age, the Shasta 
series of Early Cretaceous age, and the Upper Creta- 
ceous rocks. Similar strata, although locally not the com- 
plete sequence, occur at some places in the Coast Ranges 
of California, some as far south as Santa Barbara County. 
A few small isolated patches of parts of the Sacramento 
Valley sequence occur southwest of Redding in the 
southern part of the Klamath .Mountains province in 
California, and overlie the rocks of the Klamath .Moun- 
tains arc with marked angular unconformity. In the 
northern part of the Klamath Mountains province, chiefly 
in southwestern Oregon, the rocks of the Klamath Moun- 
tains arc are unconformablv overlain by many patches 
of strata equivalent to the Sacramento Valley sequence. 

The area of deposition of the strata of the Sacramento 
Vallcv sequence appears to have increased during the 
Cretaceous. The Knoxville formation is found only along 
the west side of the Sacramento Valley, and as patches 
within the Coast Ranges of California and the western 
part of the Klamath Mountains province of Oregon. The 
Cretaceous strata are found in the same general areas as 
the Knoxville, but in addition they underlie a much 
greater area of the Sacramento Valley and were de- 
posited over much of the Klamath .Mountains province 
of both Oregon and California. The strata of the Sacra- 
mento Valley sequence were deposited after the develop- 
ment of the Klamath Mountains arc, after metamorphism 
of the Galice formation of middle Late Jurassic (late 
Oxfordian to middle Kimmeridgian) age, and after in- 
trusion of the granitic rocks that occupy large areas in 
the Klamath Mountains province. 






19601 



Northern Coasi Ranges v\i> kiwum Mountains 



31 






j>*». 









P o J. Distant view of the Coast Ranges, looking west from U, S. Highway 99 a few miles south of Willows in the Sacramento 

Valley. Strata of the Sacramento Vallej seouence form the low strike-ridges in rlu- middle distance, and generally dip ;it moderate 
angle toward the observer. Hie mountains beyond the low ridges arc of the Coast Ranges, and are chiefly metamorphosed Fran- 
ciscan i "- 1 formation. 



Rocks that commonly are referred r<> as the Franciscan 
formation occupj large areas in the northern and central 
( !oasi Ranges of California and smaller areas in the south- 
ern Coast Ranges of California. Similar rocks in the 
Klamath Mountains of southwestern Oregon have been 
included in part of the Myrtle formation of Diller. The 
Franciscan formation consists largeh of graywackes and 
shales that arc megascopically similar to some of the 
Sacramento Vallc\ sequence. Manx of the sedimentary 
strata of the Franciscan formation, however, are inter- 
bedded with considerable quantities of chert and volcanic- 
rocks, and locallx the Franciscan includes limestone and 
glaucophane schist. In some areas the rocks of the Fran- 
ciscan formation have been metamorphosed weakly. 
( icncrallv the chert, volcanic rocks, and limestone arc 
the features that serve to identify the Franciscan for- 
mation, although areas of rocks that are mapped as Fran- 
ciscan formation range from those that include large 
quantities of chert and volcanic rocks to those in which 
little or no chert or volcanic rock is present. In areas of 
little or no chert and volcanic rocks, obvious difficult) 
arises in distinguishing graywackes and shales of the 
Franciscan formation from megascopically similar rocks 
of the Sacramento Valley sequence, particularly in areas 
where the rocks are deeply weathered or poorl) exposed. 

1 he age of the Franciscan formation and its relation 
to the strata of the Sacramento Valley sequence is not 
clear. I he Francisan formation appears likely to be older 
than most if not all of the strata of the Sacramento Valley 
sequence if one judges from the relatively greater de- 
formation, the general pattern of distribution, and cer- 
tain compositional differences of the Franciscan forma- 
tion with respect to the strata of the Sacramento Valley 
sequence. On the other hand, most of the few fossils 
found in rocks assigned to the Francisan formation are 
similar to those found in the various subdivisions of the 



Sacramento Valley sequence, ami they indicate that at 
least part of the Francisan formation spans a period of 
geologic time comparable to that of the Sacramento 
Valley sequence. 

Previous to the present reconnaissance, the northern 
Coast Ranges were generall) considered to be chiefly the 
Franciscan formation (for example see Taliaferro, 1943, 
p. 187 anil tig. 2). During the reconnaissance, however, 
the northern Coast Ranges were subdivided essentially 
into three northward-trending belts (tig. 3): a coastal 
belt that consists chiefly of graywacke ami shale; a cen- 
tral belt that includes chiefly graywacke, shale, chert, 
and volcanic rocks, and thus is like typical Franciscan 
formation; ami an eastern belt that consists of weakly 
metamorphosed rocks referred to as metamorphosed 
Franciscan formation. Within the central belt, areas solely 
of detrital rocks, as well as those of weakly metamor- 
phosed rocks, were outlined insofar as possible. 

The rocks of all three belts were indicated as Fran- 
ciscan group(?) on the preliminary geologic map 
(Pacific Southwest Field Committee, 1955, pi. 1), al- 
though it was recognized that onl) the interbedded 
graj wacke, shale, chert ami volcanic rocks of the central 
belt, might be referred to firmly as the Franciscan rocks. 
The rocks of the coastal belt of detrital sedimentary 
rocks, as well as the rocks of the smaller areas of detrital 
rocks within the central belt, were of questionable affilia- 
tion with the Franciscan. The rocks of all three belts 
previously (Taliaferro, 1943, p. 1S7, and fig. 2) had 
been considered Franciscan, and the writer had no firm 
basis for designating them otherw ise. 

Following completion of the interagency phase of the 
work, however, the graywackes of the three belts, and 
those of the Sacramento Valley sequence, were studied 
by Bailey and Irwin (1959) to determine whether the 
formational affiliation of the graywackes might be deter- 



32 



California Division of Minis 



I Bull. 179 




'hoto 4. Strike ridges of eastward-dipping strata of Jurassic and Cretaceous age along the west side of the Sacramenti 

Valley. Aerial view looking northeast. 



mined by their content of potassium feldspar. The study 
showed that the gravwackes of the typical Franciscan 
of the central belt, as well as the metamorphosed Fran- 
ciscan of the eastern belt, generally contain little or no 
potassium feldspar. The gravwackes of the Sacramento 
Valley sequence, as well as those of the coastal belt and 
some isolated areas within the general boundaries of the 
central belt, generally contain significant quantities of 
potassium feldspar. On the basis of potassium feldspar 
content, and the general lack of interbedded chert and 
volcanic rocks, the strata of the coastal belt are not now 
considered to be part of the Franciscan formation. They 
appear to be more closely related to the Sacramento 
Valley sequence. 

Strata Along the West Side of the Sacramento Valley 

Strata exposed in a northerly trending belt along much 
of the west side of the Sacramento Valley represent a 
nearly continuous record of sedimentation from late Late 
Jurassic (middle Tithonian) to Late Cretaceous. The part 
of the belt shown on the geologic map (pi. 1) extends 
a distance of about 50 miles from near Wilbur Springs to 
a point southwest of Redding in southern Shasta County, 
and is less than 10 miles in average width of outcrop. 
Along the southern and central parts of the belt the strata 
are separated from the rocks of the northern Coast 
Ranges by a band of ultramafic rocks, but along; the 



northern part of the belt they unconformably overlie the 
rocks of the Klamath Mountains arc. Along the eastern 
side of the belt the strata dip under a mantle of Tertiary 
and Quaternary rocks. 

The strata consist of interbedded sandstone, shale, and 
conglomerate, and in general thev dip eastward (photo 
4). Major folds in the strata generally are broad and are 
parallel to the northerly trend of the belt. The strata 
constitute a section that is about 35,000 feet thick. Be- 
neath the cover of younger sedimentary deposits of 
Sacramento Valley, the older parts of the section pinch 
out successively to the east, so that on the east side of the 
Sacramento Valley, a distance of about 35 miles, only 
strata of Late Cretaceous age are present. The strata of 
the Sacramento Valley sequence are fossiliferous at many 
places, and their orderly succession serves as a base with 
which to correlate the disarranged lithologic elements of 
the northern Coast Ranges and Klamath .Mountains which 
at a few places contain similar fossils. 

The section has been subdivided into three major units 
(see Anderson, 1933): the Knoxville formation of late 
Late Jurassic (middle Tithonian) age, the Shasta series 
of Fail) Cretaceous age, and the L T pper Cretaceous strata. 
The Shasta series has in turn been divided into lower and 
upper parts, the Paskenta and Horsetown formations, re- 
spectively. These divisions of the Sacramento Valley 



I960 I 



Northern Coast Ranges and Klamath Mot ntains 

^•^■■■■■ir 



33 





&»*> 







1 \ 




I 



Photo 5. Thin bedded shale, sandstone, and conglomerate of the Knoxville formation, dipping eastward near Stonj ford. 



sequence have been given group or formational status 
by various geologists and by the U. S. Geological Survey, 
but -with the possible exception of the Knoxville forma- 
tion they are differentiated chiefly on a fauna] rather 
than a lithologic basis. 

Knoxville Formation. Tbc Knoxville formation as 
exposed along the west side of the Sacramento Valley 
between Wilbur Springs and Paskenta is about 10,000 
feet thick. The base is not known with certainty, as along 
most of the valley the lowest exposed beds are in fault 
contact with the band of ultramafic rocks. The outline 
of the Knoxville formation is inferred north of a fault 
zone that trends northwest across strata of the Sacra- 
mento Valley sequence at latitude 40 degrees north (pi. 
1), and although the Cretaceous parts of the Sacramento 
Valley sequence arc known to be present north of Bee- 
gum Creek, it is not known with certainty that the 
Knoxville is represented. The northernmost exposure of 
rocks referred to the Knoxville by Anderson (1945, p. 
926-927) is on the northeast slope of Tedoc Peak, at the 
southern boundary of the Chanchelulla Peak quadrangle, 
where he states that basal conglomerate of the Knoxville 
formation rests directly on the so-called Klamath com- 
plex. 

The Knoxville formation generally consists of a thick 
section of thin-bedded shales with thin lenses of lime- 
stone, but interbedded graywacke and conglomerate are 
locally abundant (photo 5). Fossils indicate that it is late 
Late Jurassic (middle Tithonian) in age, and one of its 
most characteristic and abundant species is Buchia piochii 
(Gabb). 

2— 1S730 



The contact between the Knoxville formation and the 
overlying Shasta series is marked by a fairly abrupt and 
complete change in fauna, by lenses of conglomerate at 
many places, and by broad structural conformity. 

Shasta Scries. The strata referred to the Shasta series 
have a higher ratio of graj wacke to shale than has the 
Knoxville formation. The average thickness is about 
10,000 feet, divided about equally between lower and 
upper fauna! divisions, the Paskenta and Horsetown for- 
mations. The Shasta series contains a variety of mega- 
fossils (Anderson, 1938) as well as microfossils, and 
locally the fossils are abundant. One species characteristic 
of the Paskenta formation is Buchia crassicollis ( Key- 
serling), which represents the older Early Cretaceous 
(Valanginian). It is specifically mentioned as it also is 
found in some rocks of the northern Coast Ranges. 

The term Shasta series has generally been considered to 
include only Lower Cretaceous strata, but along much 
of the west side of the Sacramento Valley there has been 
little agreement as to where the contact between the 
Shasta series and Upper Cretaceous strata should be 
placed. This lack of agreement casts considerable doubt 
as to the validity of a hiatus many early workers have 
postulated between the Lower and Upper Cretaceous, 
and as noted by Kirby (1943, p. 289) there is no great 
structural' discordance or specific evidence of a great 
hiatus separating the Shasta series and the Upper Cre- 
taceous rocks of the Sacramento Valley area. Some 
geologists have placed the contact at the base of the 
Venado formation of Kirby (1943, p. 282, 287), as is 
shown on the geologic map (pi. 1), while others have 



34 



California Division of .Mines 



Bull. 




Photo 6. Quarry in eastward dipping sandstone of Late Cretaceous age, near Sites. Some thin interbeds of sandstone and shale 

pinch out, down dip. Man circled for scale near center of photo. 



placed it lower in the section at the base of a conglom- 
erate member. The conglomerate member and the 
Venado formation are separated by several thousand 
feet of shale. 

Lower Upper Cretaceous. Upper Cretaceous strata 
along the west side of the Sacramento Valley consist of 
sandstone and shales (photo 6) and are about 15,000 feet 
thick. They commonly have been referred to as the 
Chico formation (see Kirby, 1943, p. 281), although they 
range from the Cenomanian through the Campanian in 
age whereas the type Chico formation on the east side 
of the Saramento Valley ranges from the middle Conia- 
cian to the middle Campanian in age. 

Rocks of the Northern Coast Ranges of California 

The northern Coast Ranges of California consist 
chiefly of sedimentary and volcanic rocks that range 
from late Late Jurassic (middle Tithonian) to early 
Late Cretaceous (Cenomanian) in age. The area has been 
subdivided into three principal lithic belts that trend 
northwesterly; a central belt of sedimentary and volcanic 
rocks of the Franciscan formation, an eastern belt of 



weakly metamorphosed Franciscan formation (? ), and a 
coastal belt of undivided sedimentary rocks. Relatively 
small areas of rocks of the eastern and coastal belts occur 
within the central belt. 

Franciscan Formation of the Central Belt. The sedi- 
mentary and volcanic rocks of the central belt of the 
northern Coast Ranges of California appear similar to 
those exposed on the San Francisco Peninsula in the cen- 
tral Coast Ranges that were named the Franciscan series 
by Lawson (1895, p. 407). They also are similar to part 
of the Myrtle formation of Diller (1898) in the western 
part of the Klamath Mountains province of Oregon. 

The Franciscan formation is a eugeosynclinal accumu- 
lation of detrital sedimentary rocks, chemical sedimen- 
tary rocks, and volcanic rocks. The detrital sedimentary 
rocks are chiefly graywacke with interbedded shale and 
minor conglomerate. The chemical sedimentary rocks 
are rhythmically thin-bedded chert and minor foraminif- 
eral limestone. The volcanic rocks include flows and 
pyroclastics, largely of basaltic or spilitic composition, 
and are altered to greenstones. In addition, the Franciscan 
formation includes small masses of glaucophane-bearing 



• 



I960 



Northern Coast Ranges wi> Kiwiwii Mountains 



J 5 



schists. General]) the rucks of tlic Franciscan formation 

are sheared, deformed, and dislocated, and arc intruded 
widely by mafic and ultramafic rocks. Owing largely to 
its seemingly chaotic character, the Franciscan formation 
has defied satisfactory interpretation of its role in the 
geologic history of the Pacific Coast region. 

Graywacke is the dominant rock of the Franciscan 
formation. It is a fine- to coarse-grained, well indurated 
rock, and fresh specimens range in color from dark gray 
to greenish gray. The graj \\ acke weathers to shades of 
dark-brown to light-buff, and in some places where 
weathering has been particularly intense the rocks are 
friable. The grains that constitute the graywacke are 
mostl) angular and subangular, and arc mainly frag- 
ments of quartz, plagioclase feldspar, chert anil volcanic 
rocks. Some specimens contain a few grains, less than a 
tenth of a percent, of potassium feldspar, but most con- 
tain no potassium feldspar (Bailey and Irwin, 1959). A 
fine-grained matrix constitutes a small percentage of most 
specimens. Calcite is rarely present in the graywacke. 

The graywacke forms beds that range from a fraction 
of an inch to more than 10 feet in thickness, but most 
commonly the thickness is between 1 and 3 feet. Bedding 
planes generally are sharp. Most of the beds are even- 
grained, but at some places the sediments grade upward 
from coarse to fine grained. Dctrital shale fragments are 
seen in some beds of graywacke at most exposures 
throughout the northern Coast Ranges. They most com- 
monly occur in vaguely delineated zones in a bed of 
graywacke that perhaps otherwise is even-grained, but 
at other places appear to be randomly distributed. The 
shale fragments arc mostly flattened ellipsoids, but tabu- 
lar fragments that appear to have been transported only 
short distances do occur. The shale fragments are com- 
monly about a quarter of an inch in longest dimension. 

Fossils were found in the graywacke at locality no. 6 
(pi. 1). The locality is in wV,NW'/ 4 sec. 10, T. 20 N., 
R. 12 \\\. about 100 feet east of a cattle guard at the 
south end of Eden Valley in central .Mendocino County. 
Only one of the fossils appeared sufficiently well pre- 
served to warrant being collected; the others were small 
fragments scattered abundantly throughout some of the 
graywacke. The best preserved specimen was examined 
by R. W. Imlay. who states (written communication. 
1956) that it is an external mold of a right valve of an 
aucella, ami that it is too poorly preserved to be identi- 
fied specifically. The graywacke containing the fossil 
was tested by the staining method (Bailey and Irwin. 
1959) and was found to contain no potassium feldspar. 

Shale is interbedded with graj w acke as layers that 
range from thin partings to beds several hundred feet 
thick. In places shale is rhythmically interbedded with 
fine-grained graywacke, and elsewhere with chert. The 
shale ranges from black to greenish gray. Fragments of 
fossil plants are locally abundant on bedding surfaces. 
particularly in shale partings between beds of gray- 
wacke, and in some shale the arenaceous tests of marine 
micro-organisms have been found. 



Conglomerates constitute only a small percentage of 
the bulk of the detrital rocks, but locally are abundant. 
The fragments range from fine pebbles to boulders as 
much as a foot in diameter, but pebbles and small cobbles 
are most common. The pebbles are dominantly rccrystal- 
lized chert, greenstone, and fine-grained porphyritic 
rocks. Most of the conglomerate beds are only a few 7 
feet thick, particularly the finer pebble conglomerates, 
but some are several tens of feet thick. At a few places, 
sections of dctrital rock consisting largely of conglom- 
erate arc at least several hundred feet thick. Beds of 
boulder conglomerate seem most abundant in sections 
containing considerable chert and greenstone. 

The chert generally is abundant in the vicinity of vol- 
canic rocks. It is characteristically red-brown or green, 
and rhythmicall\ interbedded with thin shale layers. The 
individual chert beds range from a fraction of an inch to 
several inches in thickness. Some lenses of rhythmically 
bedded chert appear to be several hundred feet thick and 
more than a mile long, but most are considerably smaller. 
Distortion of manv chert sections is indicated by chevron 
folds with amplitudes that range from several inches to 
several feet (photo 7). Fossil radiolaria arc found in much 
of the chert, but well-preserved remains are not abun- 
dant. As the chert is nearly always close to volcanic rock, 
a genetic relation between the chert and the volcanics 
is probably r indicated. 

Limestone has been found in the northern Coast 
Ranges at few localities in areas of the Franciscan forma- 
tion. Some of the limestone lenses are similar to the Calera 
limestone member described by Lawson (1895 and 1914) 
as part of the Franciscan formation on the San Francisco 
Peninsula, and are likewise similar to the Whitsctt lime- 
stone described by Diller (1898) as part of the Myrtle 
formation in the Klamath Mountains of Oregon. These 
lenses of limestone characteristically arc thin-bedded and 
contain interbedded chert layers, volcanic debris, and 
locally abundant foraminifera. 

The best known locality of foraminifera] limestone in 
the northern Coast Ranges is near Laytonville, where it 
is exposed in several road cuts (locality no. 7, pi. 1) on 
Highway 101 about % mile north of the village. It is 
also exposed 2 miles north of Laytonville, about 200 feet 
northeast of Highway 101 where the limestone forms a 
prominent hillock in a grassland area (locality no. 8, 
pi. 1). These exposures have been referred to bv Diller 
(1902, p. 65-66), Thalmann (1943) and Taliaferro (1943. 
p. 193). The limestone near Laytonville is thought to be 
part of a stratigraphic section that includes chert and 
volcanic rocks as well as detrital sedimentary rocks, but 
the section is not clearly- exposed. The contact between 
the limestone and adjacent strata was seen at only* one 
place, and there the limestone is underlain by fine-grained 
graywacke. The limestone is thinly bedded, ranges from 
pink to pale red-brown in color, and contains many thin 
layers of reddish chert. At one place a minimum thick- 
ness of 12 feet of limestone is exposed, but exposures 
are such that the total thickness is not known. 



36 



California Division of Mines 



[Bull. 179 



- ■ . 




b* ft* ■' *-i ? 

I-' 'If & -fit 
( i ' 7 ; it 



%■ # v;- */ • >r / • '4 1 -^k^--* a- \ • t v-. # fJL. '/••*# i 



K ft* 



Photo 7. Folded clicrt of the Franciscan formation, between Dos Rios and Covelo. 



Similar foramini feral limestone crops out (locality no. 
9, pi. 1) in SW l / 4 sec. 9, T. 3 S., R. 2 E., about 12 miles 
northwest of Garberville in southern Humboldt County. 
It is exposed as an isolated knob in a general area of 
sheared rocks of the Franciscan formation and serpentine 
(E. H. Bailey, oral communication, 1954). 

Abundant microfossils are found in the limestones near 
Laytonville and Garberville, as well as in bodies of similar 
limestone found elsewhere in the Franciscan formation 
and in the Myrtle formation (Thalmann, 1942 and 1943; 
Cushman and Todd, 1948; Walker, 1950; Church, 1952; 
Glaessner, 1949; Kiipper, 1955; and Thalmann, 1957, 
written communication). According to Taliaferro (1943, 
p. 193), radiolaria found in the chert associated with the 
foraminiferal limestone are the same type as those found 
in chert elsewhere in the Franciscan formation. 

Thalmann (1943) first considered the foraminiferal 
limestones of the Franciscan and Myrtle formations to 
be synchronous deposits of Turonian age. However, on 
the basis of later study he (Thalmann, written communi- 
cation, 1956) considers the Calera limestone member on 
the San Francisco Peninsula to be of Cenomanian age, 
and the limestones near Laytonville and Garberville to be 



slightly older, that is. Late Albian or possibly earliest 
Cenomanian in age (see Irwin, 1957, p. 2290). 

Limestone that differs from the foraminiferal lime- 
stones crops out (locality no. 5, pi. 1) about 3 miles 
south of Sheetiron Mountain and a quarter of a mile east 
of Bowery Flat in the northwestern part of the Stony- 
ford quadrangle (fig. 2). The limestone is finegrained 
and light-gray in color. It occurs as beds that range from 
Yi to 1 foot in thickness, and as nodules, interbedded 
with graywacke and shale. Pillow basalt nearby appears 
to be part of the stratigraphic section. Graywacke col- 
lected from the locality contains no potassium feldspar. 
Fossils were found at several places in the shale. They 
were referred to R. W. Imlay of the U. S. Geological 
Survey, who states (written communication, 1956) that 
they are Buchia crassicollis (Keyserling) of early Early 
Cretaceous (middle to late Valanginian) age (see Irwin, 
1957, p. 2293). 

Limestone occurs (locality no. 4, pi. 1) at the north 
end of McLeod Ridge at the south shore of Lake Pills- 
burv, but it is questionable whether the limestone here 
is really a part of the Franciscan formation. The lime- 
stone is massive and is light-gray in color. It occurs as 



1960] 



Northern Coast Ranges \\i> Imwiuh Mountains 



37 



beds that range from ' j to 1 toot in thickness in dark 
greenish gray shale. The rocks are sheared, and the lime- 
stone beds are broken into segments a tew feet long. 
Fossils are unusually abundant ami well preserved in 
both the limestone and the shale. They were submitted 
to R. \V. Imlav. wlm states (written communication, 
1953) that they are Buchia piochii (Gabb) of bare Ju- 
rassic (middle Tithonian) age. Chert and volcanic rocks, 
generally considered characteristic of the Franciscan 
formation, were not seen to be interbedded with the 
nnks. ami the limestone and shale may belong to the 
Knoxville formation rather than to the Franciscan. 
Limestone has been found (locality no. 16, pi. 1) about 
miles east-northeast of Eureka, in sees. 13 and 14, T. 5 
N., R. 1 E., on the northeast side of Jacoby Creek at an 
altitude of about 400 feet. It has been described by Aver- 
ill (1941, p. 516) and Rice (oral communication, 1955) 
as probably of the Franciscan formation, but the field 
relations apparently arc not clear. Most of the limestone 
is thought to be nonfossiliferous, but a specimen given 
to the writer by O. E. Bowen, Jr., of the California Divi- 
sion of Mines, contains abundant fossils. The specimen 
was examined by the late J. 1!. Reeside of the U. S. Geo- 
logical Survey, who reported as follows: 

"The fossils in this piece of rock appeal to be the comminuted 
fragments of one species of large pelecypod. Some of them bear 
fragments of the hinge and suggest very strongly a species of 
Glychneris or Idonearca. It would lie very difficulr to prove the 
age of the specimen, but I would guess it to be Upper Cretaceous. 
Ralph [mlay and David Nicol have examined the specimen also, 
and think this opinion not unreasonable." 

In the central part of the Alderpoint quadrangle, lime- 
stone is reported (Averill, 1941, p. 518) in sees. 20 and 
29, T. 4 S., R. 5 I .. near Harris. It crops out as a cliff 
}5 feet long and 10 feet high, and smaller exposures are 
found at intervals for a quarter of a mile. Judging from 
its reported location, the limestone occurs in an area of 
the Franciscan formation. 

Manning and Ogle (1950. p. 21) mention only a few- 
small lenses of thoroughly recrystallized, dense, dark- 
gray limestone in the Franciscan formation in the Blue 
Lake quadrangle (\\<a.. 2). In the Eel River Valley area. 
Ogle ( 1953, p. 82) describes a bed of limestone 75 feet 
thick that can be traced for perhaps half a mile. On the 
geologic map of the area (Ogle, 1953, pi. 1) it is shown 
as 2 miles in length, in sees. 16, 9, 8, and 5, T. 1 X., 
R. 1 W., about 5 miles southwest of Rio Dell, crossing 
the False Cape shear zone. The limestone may belong to 
the Franciscan formation; it has not been examined by 
the writer. 

Volcanic rocks are abundant throughout much of the 
Franciscan formation. Most of the volcanic rocks have 
been altered to greenstone. They probably are the ef- 
fusive product of submarine volcanic activity, as pillow 
structures, vesicles and agglomeratic textures are seen at 
many localities, and as they are widely associated with 
detrital and chemical marine sedimentary rocks. At main 
places, however, structures and textures that identify 
their origin arc not seen, and some of the greenstone may 
be intrusive. 



The volcanic rocks generall) are altered rocks of mafic 
composition. They generally are highly fractured. Ac- 
cording to Taliaferro (1943, p. 145) who has studied 
similar rocks elsewhere in the Const Ranges, the volcanic 
rocks have been subjected to alteration, such as spiliri/a- 
tion, that is thought to have been penecontemporaneous 
with extrusion of the originalh basaltic rocks. I he areas 
of volcanic rocks are generally characterized by dark 
red-brown soil and scrubby vegetation. 

Small bodies of schist that contain glaucophane and 
other uncommon metamorphic minerals such as lawson- 
ite and pumpellyite are found at many places in the 
Franciscan formation. They are similar to those that have- 
been described at length (Taliaferro, 1943, p. 1 59- 1 s2 ) 
elsevi here in the Coast Ranges. The schist is characteristi- 
cally gray-blue in color, and fresh surfaces of foliation 
have a bright sheen. It is a tough, resistant rock, and is 
most commonly found as isolated and seemingly un- 
related bodies in zones of intense shearing. In most cases. 
metamorphism has destroyed the character of the rock 
from which the schist has been formed, but a few exam- 
ples of schist were found that appear from their texture 
and field relations to have been formed from graywacke, 
shale, greenstone, and chert. 

Many of the bodies of schist appear to be crudely len- 
ticular in shape, and range from perhaps ten to several 
tens of feet in length. Larger bodies, however, arc not 
rare. By far the largest body of glaucophane and related 
schist in the northern Coast Ranges trends northwest- 
erly through the western part of the Hcaldsburg quad- 
rangle (see Gealey, 1951, pi. 1) and across the Skaggs 
Springs quadrangle (fig. 2). It is more than 15 miles in 
length and about a mile in width. 

Most localities of glaucophane schist seen by the 
writer are areas of poor exposure, and contact relations 
have not been observed. It seems likely, however, that at 
most places the contacts are faults and are sharp, for in 
most cases the rocks exposed nearest to the schist are 
sheared but are otherwise normal graywacke, shale, 
chert, and volcanic rocks. According to Taliaferro (1943. 
p. 168) the glaucophane and related schists are the result 
of pneumatolytic metamorphism by emanations accom- 
panying the intrusion of mafic and ultramafic rocks. This 
concept apparently is substantiated by observations by 
C. W. Chesterman (oral communication, 195") near the 
crest of Leech Lake Mountain in the northeastern part 
of the Covelo quadrangle (fig. 2), where glaucophane 
has been developed in graywacke adjacent to unusually 
well-exposed sills of ultramafic rocks. .Much of the glau- 
cophane schist seen during the present reconnaissance, 
however, is remote from outcrops of ultramafic rocks. 

Metamorphosed Franciscan(?) Formation of the East- 
cm Belt.. An assemblage of weakly metamorphosed 
rocks, chiefly slates and phyllites that tentatively are con- 
sidered to be a part of the Franciscan formation, forms 
a high range along the west side of the Sacramento 
Valley, and smaller areas of similar rocks are found in 
the central belt of the Coast Ranges. The high range ex- 



38 



California Division of Mines 



[Bull. 179 



tends northward approximately 80 miles from near 
Wilbur Springs in western Colusa County to the south- 
ern part of the Klamath Mountains province in western 
Tehama and southeastern Trinity Counties. The trend of 
the range is northward, nearly parallel to the Sacramento 
Valley, rather than parallel to the general northwesterly 
grain of the Coast Ranges elsewhere. The eastern bound- 
ary of the area of metamorphosed rocks is a band of 
serpentinized ultramafic rocks that separates the meta- 
morphosed rocks from the nonmetamorphosed Knoxville 
formation of the Sacramento Valley. The western bound- 
ary is not so clearly defined, but for much of its length 
along the west face of the range it is mantled by land- 
slide, and probably is a fault. Along the western bound- 
ary, the mildly metamorphosed rocks are in contact with 
nonmetamorphosed rocks of the Franciscan formation. 

Several smaller areas of similar metamorphic rocks 
within the central belt of Franciscan rocks trend north- 
west, parallel to the general grain of the Coast Ranges 
but diverging at an angle of approximately 20 degrees 
from the trend of the eastern belt. The largest of these 
is 30 miles long, and extends northwest from the south- 
east side of Clear Lake to the eastern part of the Porno 
quadrangle (fig. 2). Another extends northward from 
near Hull Mountain in the southwestern part of the Hull 
Mountain quadrangle (fig. 2) to the east side of Covelo 
in the Covelo quadrangle. The only other area shown on 
the geologic map (pi. 1) is in the western part of the 
Hoaglin and the southwestern part of the Blocksburg 
quadrangles, but relatively small areas of rocks that have 
been subject to a similar degree of metamorphism are 
found elsewhere in the Coast Ranges, both in the report 
area as well as in the central Coast Ranges. 

Neither the lithology nor degree of metamorphism is 
uniform in the areas of metamorphic rocks. The eastern 
belt probably could have been subdivided during the 
present reconnaissance into: (a) areas of detrital rocks, 
and (b) areas of detrital rocks, chert, and volcanic rocks. 
Owing to a scarcity of roads, however, few traverses 
were made through the area. The area also is densely 
forested and not amenable to photo interpretation. Prob- 
ably it is composed chiefly of weakly metamorphosed 
sandstones and shales. Between the latitudes of Sheetiron 
Mountain and Anthony Peak, cherts and greenstones are 
uncommon except in the vicinity of Anthony Peak and 
at Black Butte in the northeastern part of the Hull 
Mountain quadrangle. To the north and south, however, 
chert and greenstone are locally abundant in the eastern 
belt. Chert and greenstone also occur with the metamor- 
phosed detrital rocks of the smaller areas within the cen- 
tral belt of the northern Coast Ranges. Thinly bedded 
chert is abundantly interbedded with slaty detrital rocks 
in the southwestern part of the Bartlett Springs quad- 
rangle, and is particularly well exposed along the high- 
May for a few miles west of Clearlake Oaks. Crenulated 
and phyllitic detrital and volcanic rocks are abundant in 
the vicinity of Hells Half Acre in the west-central part 
of the Hull Mountain quadrangle. 



Although the rocks are chiefly slates and phvllites, 
they range from rocks in which foliation is weak to 
coarse mica schist and greenschist. At some places the 
foliation is so weakly developed that decisions as to 
whether the rocks should be mapped as part of the meta- 
morphic assemblage were arbitrary. Indeed, at some lo- 
calities the metamorphic rocks appear to grade into non- 
metamorphosed rocks similar to the sedimentary and 
volcanic rocks of the Franciscan formation of the central 
belt. 

A considerable difference in degree of development of 
slaty cleavage commonly is evident between relatively 
fine- and coarse-grained sedimentary rocks of the eastern 
belt. At many places, slate is interbedded with graywacke 
that shows only a slight platy structure. Conglomerate 
beds, seen at a few localities, generally show little evi- 
dence of metamorphism, but in the vicinity of Mendo- 
cino Pass south of Anthony Peak, conglomerate beds 
contain pebbles that are stretched. A mile or two south 
of the Pass, however, the rocks are more highly meta- 
morphosed, and coarse mica schist and greenschist are 
abundant (photo 8). 

Fossils were found at only one locality in the eastern 
belt of metamorphosed Franciscan formation(?) (local- 
ity no. 1 3, pi. 1 ) during the present reconnaissance. The 
locality is on the trail between The Knob and Dogleg 
Peak along the crest of the main drainage divide in the 
west-central part of the Yolla Bolly quadrangle (fig. 2). 
It is at an altitude of 5,900 feet in NW'/ 4 sec. 11, T. 26 
N., R. 10 W., on the crest of a small spur that extends 
southwest from the main ridge. The fossils are in lime- 
stone, and although the limestone was not seen in place, 
it seems unlikely that the float has traveled far owing to 
its position on the crest of the spur, only a short distance 
from the crest of the main divide. The fossils were identi- 
fied by R. W. Imlay as Btichia crassicollis (Keyserling) 
of earlv Early Cretaceous (Valanginian) age (see Irwin, 
1957, p. 2292-2293). 

Fossils are reported by Taliaferro (1943, p. 190) from 
two localities in the principal belt of the metamorphic 
assemblage. One locality is on the Paskenta-Covelo road 
east of Anthony Peak, and the other is on a Forest Serv- 
ice road about 2 miles north of Black Diamond lookout 
station. According to Taliaferro, the fossils are similar 
to buchias found elsewhere in the Franciscan and Knox- 
ville, but unlike those in the Mariposa slate of the Sierra 
Nevada. 

The Franciscan formation is nowhere known to be in 
depositional contact with older formations. Along the 
western boundary of the Klamath Mountains province 
the Franciscan is in fault contact with schists that are 
probably a metamorphic facies of the Galice formation 
of middle Late Jurassic (late Oxfordian to middle Kim- 
meridgian) age. In the Coast Ranges south of San Fran- 
cisco Bay the Franciscan formation is in fault contact 
with metamorphic rocks of the Sur series of Paleozoic (?) 
age that have been intruded by plutonic rocks. Accord- 



I960! 



Northern Coast Ranges and ki wiun Aim \iu\s 



39 



S** 




Pimm s. Contortei 



losed Franciscan(P) formation, with quartz veinlets. Locality about 5 miles 
southeast of Anthonv Peak. 



ing to Taliaferro (1943, p. 186) abundant debris from 
those two units is found in the Franciscan formation. 

Data regarding the age of the Franciscan formation are 
conflicting. The Franciscan is considered by Taliaferro 
( 1943) to he Fare Jurassic in age, and to grade upward 
into the Knoxville formation. At various places in the 
Coast Ranges of California, detrital strata of Early Cre- 
taceous age are considered to lie unconformably on the 
Franciscan formation. On the other hand, fossils found 
in rocks generall) considered to he Franciscan, in the 
type area and elsewhere, are of the same species as fossils 
found in st lata of the several subdivisions of the Sacra- 
mento Valley sequence, and they indicate that at least 
some of the rocks assigned to the Franciscan formation 
range from late Fate Jurassic (middle Tithonian) to 
early Fate Cretaceous (Cenomanian) in age. The paleon- 
tologic evidence has been summarized recently by the 
writer (Irwin, 1957). Few fossils have been found in 
rocks of the Franciscan, how ever, and much of the Fran- 
ciscan formation may well be older than the Knoxville 
formation. 



The geographic distribution of the foramini feral lime- 
stones, the youngest rocks assigned to the Franciscan in 
which fossils have been found, is suggestive of strati- 
graphic and structural significance but the significance 
is not yet understood. It is noteworthy that the forami- 
nifcral limestones have been found only along the south- 
west side of the belt of the Franciscan formation of the 
central and northern Coast Ranges of California, and 
have not been reported in the southern Coast Ranges. 
The most obvious implication is that the younger part of 
the Franciscan formation occurs chiefly along the south- 
west side of the belt of Franciscan. 

The results of stain tests for potassium feldspar (Bailey 
and Irwin, 1959) indicate that most of the graywackes 
of the Franciscan formation of the northern Coast 
Ranges contain no potassium feldspar, or less than a tenth 
of a percent potassium feldspar. A few specimens con- 
tained appreciable quantities of potassium feldspar, but 
these may have come from other lithic units that were 
erroneously included in the Franciscan. The graywackes 
of the Sacramento Valley sequence show a significant 



40 



California Division of Mines 



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* Interpreted by the writer on the basis that areas shown as Myrtle formation by Oilier are shown 
as Knoxville, Paskenta and Horsetown formations by Wells (1955). Relation of Rogue formation after 
Cater and Wells (1954). 



Figure 5. Chart showing changes in concept of the Myrtle, Galice ond Dothan formations of 

Diller (1903b and 1907) of southwestern Oregon and correlations with the Franciscan, 
Knoxville, Horsetown and Paskento formations of northern California. 



1960] 



Northern Coast Ranges and Klamath Mm ntatns 



41 



increase in potassium feldspar content with decreasing 
age, the Late Jurassic ranging from to 4 percent potas- 
sium feldspar, the Early Cretaceous ranging from 
less than 0.1 to 25 percent, and the Late Cretaceous 
ranging from 0.5 ro 35 percent. This suggests that in- 
creasingh large areas of potassium feldspar-hearing plu- 
tonic rocks were being exposed to erosion at the source 
area during deposition of the Sacramento Valley se- 
quence. If the graywackes of the Franciscan formation 
are considered to have been derived from the same gen- 
eral source area as those of the Sacramento Valle) se- 
quence, they would appear to be older owing to the lack 
of potassium feldspar. This concept may apply to part ot 
the Franciscan formation, hut is nor consistent with the 
lack of potassium feldspar in some graywackes of the 
Franciscan formation where fossils equivalent in age to 
those of the Sacramento Valley sequence are found. 

Problems regarding the age and formational designation 
of rocks of the Franciscan and other formations of Juras- 
sic and Cretaceous ages in the Coast Ranges of California 
arc similar to those of the M\ rtle and Dothan formations 
of Oilier (fig. 5) in the western part of Klamath Moun- 
tains of Oregon. The formations of southwestern Oregon 
have not been examined extensively in the field by the 
writer, but judging chiefly from the literature the .Myrtle 
formation of Diller seems to be a northward continuation 
of the Franciscan formation plus associated strata equiva- 
lent to the Knoxville, Paskcnta, and Horsetown forma- 
tions of the Sacramento Valley. Diller (1907, p. 411) 
considered the Myrtle formation equivalent to strata that 
in the present report are referred to as Knoxville, Pas- 
kcnta. and Horsetown formations, and noted the presence 
of interbedded chert, volcanic rocks, and foraminifcral 
limestone (Whitsett limestone). Louderback i 1905, also 
see Diller 1907, p. 412-421) reinterpreted the .Myrtle 
formation, and subdivided it into so-called upper and 
lower series. The so-called lower series, named Dillard 
scries, included the detrital sediments with interbedded 
chert and foraminifcral limestone, and was considered 
equivalent to the Franciscan formation. The so-called 
upper series, named .Myrtle group, consisted wholly of 
detrital sediments that Louderback considered to be 
younger and less well indurated than those of the Dillard 
series and presumably equivalent to those of the Sacra- 
mento Valley sequence. Taliaferro ( 1942, p. 75-77) con- 
curred largely with Louderback's subdivision of the 
Myrtle formation, but grouped the Upper Jurassic part 
of the Myrtle group with the Dillard to conform with 
his concept regarding the relation between the Franciscan 
and Knoxville in the Coast Ranges of California. 

Areas mapped as Myrtle formation by Diller (1903b) 
in the Port Orford quadrangle, Oregon, were subdivided 
into two units, presumably on a faunal basis, by Wells 
(1955), but the connotation of his two units is signifi- 
cantly different from Louderback's subdivision. One unit 
has been named the Knoxville formation, and the other 
the Paskcnta and Horsetown formations. 



In all of the correlations of the Myrtle formation of 
Diller (fig. 5), the foraminifcral limestones (Whitsett 
limestone) have not been taken into proper account. 
According to Thalmann (1943) the foraminifcral lime- 
stones of the Myrtle formation of Diller are middle Cre- 
taceous in age. Thus they are younger, rather than older, 
than most of the Cretaceous rocks considered by Louder- 
back and Taliaferro to overlie them. 

Strata younger than the Sur scries ' and older than the 
oldest (middle Tithonian) paleontologically dated part 
of the Franciscan formation have not been recognized 
in the Coast Ranges of California. The w riter has no data 
that indicate the presence of such rocks, but points to 
the possibility of their existence and the probable diffi- 
cult \ of their recognition. The sedimentary strata of the 
Dothan, Galice, and Franciscan formations are similar, 
and arc interbedded, at least locally, with chert and 
volcanic rocks. All apparently contain little or no potas- 
sium feldspar, ami fossils are rare. Differences have been 
drawn between these formations on the basis of relative 
thickness of betiding, minor differences in degree of 
lithitication and slatiness, and whether small veinlets cut- 
ring the strata are siliceous or calcareous. None of these 
criteria is absolute, and indeed all are of highly question- 
able value, as the range in thickness of bedding, and 
degree of lithification and slatiness is as great within the 
formations as between them. The validity of the fore- 
going statements was partly recognized by Diller (1907, 
p. 411). who stated that ". . . on lithologic grounds, 
therefore, the Myrtle and Dothan arc not always easily 
distinguished . . . and ... it is only by means of fos- 
sils or definite stratigraphic data having references to 
fossiliferous horizons that affords a satisfactory basis for 
separating the Dothan and Myrtle in the held.' - One 
might well question how the Dothan, Galice, and Fran- 
siscan can be distinguished from one another if they 
intermingle in a structurally complex area. 

Historically, the various conflicting correlations that 
have been made with the Franciscan formation on a litho- 
logic basis do not indicate a unique lithology. Diller 
(1907, p. 420) and Wells, Hot/, and Cater (1949, p. 9) 
consider the Franciscan formation equivalent to the 
Dothan formation. Louderback (1905, p. 547-548) and 
Taliaferro (1942, p. 89) correlate the Franciscan forma- 
tion with the Dillard series, that is, part of the Myrtle 
formation of Diller. A large area of dominantly detrital 
strata in western Del Norte County has been assigned to 
the Franciscan by Taliaferro (1943, p. 123. fig. 2), Wells, 
Cater, and Rvnearson (1946, p. 6), and Rice (data incor- 
porated in pi. 1), and the rocks of the same area are 
assigned to the Dothan by Maxson (1933, pi. 4). Along 
the boundary between California and Oregon (see fig. 3), 
rocks assigned to the Franciscan in California are con- 
tiguous with rocks assigned (Wells, 1955) to the Dothan 
in Oregon. Judging from these conflicts, the several for- 
mations apparently are not different enough, lithologi- 

1 Sux series is the name applied to quartzite, schist, and marble exposed in the 
Santa Lucia Range of the southern Coast Ranges of California. It gener- 
ally is considered to be pre-Franciscan, probably Paleozoic in age. 



42 



California Division of Mines 



[Bull. 179 



cully, to permit accurate correlation or formational des- 
ignation on only a lithologic basis. 

Coastal Belt of Undifferentiated Sedimentary Rocks. 
Sedimentary rocks crop out in a belt that extends from 
near Petrolia in southwestern Humboldt County to the 
Russian River in Sonoma County, a distance of approxi- 
mately 150 miles, and probably continue southeastward. 
The belt ranges from about 10 miles to 25 miles in 
width. North of Point Arena it is bounded on the west 
by the Pacific Ocean. Southwestward from Point Arena 
it is bounded on the west by the San Andreas fault to 
a point a few miles north of the Russian River. The 
coastal belt is bounded to the east by the central belt of 
Franciscan rocks throughout most of Sonoma and Men- 
docino Counties, and in southern Humboldt County by 
the Yager formation of Ogle (1953). Rocks similar to 
those of the coastal belt underlie relatively small areas 
within the central belt of the Franciscan formation. 

The sedimentary rocks of th; coastal belt consist 
chiefly of graywacke, shale, and minor conglomerate 
(photo 9). Stain tests show (Bailey and Irwin, 1959) that 
most of the graywackes of the coastal belt contain ap- 
preciable quantities of potassium feldspar. In this respect 
the graywackes of the coastal belt are similar to the rocks 
of the Sacramento Valley sequence, but differ from tlv: 



graywackes of the Franciscan of the central belt and the 
metamorphosed Franciscan of the eastern belt. 

Volcanic rocks interbedded with graywacke and shale 
are found at a few places in the coastal belt and appar- 
ently are most abundant in the southern third of the belt. 
Small areas of pillow basalt, greenstone, and chert were 
seen at a few places along the Stewarts Point-Skaggs 
Spring road. Greenstone occurs over an area of 2 square 
miles east of Comptche in the southeastern part of the 
Glenblair quadrangle (fig. 2), and also 3 miles southeast 
of McDonald Ranch in the central part of the quad- 
rangle. Greenstone associated with small lenses of lime- 
stone 3 Vi miles northeast of Usal in the Piercy quadrangle 
is reported by Trask and others (1943, p. 80). Layers 
of pillow basalt are known in the west-central parts of 
the Point Delgada and Scotia quadrangles (fig. 2). Con- 
sidering the dense vegetation and poor exposure in the 
coastal belt, areas of volcanic rocks other than those seen 
are likely present, but the total quantity of volcanic rocks 
doubtless is very small compared with sedimentary rocks. 
Nevertheless, these few known areas of volcanic rocks 
apparently document volcanism contemporary with dep- 
osition of potassium feldspar-bearing graywacke. 

Limestone occurs at a few places in the coastal belt 
and in the smaller areas of similar rocks within the cen- 




Photo 9. Thick beds of 



;raywacke of the coastal belt of undifferentiated sedimentary rocks, along U. S. Highway 101 about a mile 

west of Cummings. 



1960] 



Northern 0>\m Ranges and Klamath Mountains 



43 



tral belt of the Franciscan formation. One of the most 
interesting occurrences of limestone (fossil locality no. 
2. pi. 1 ) in the coastal belt is on the north bank of the 
Gualala River, opposite the YMCA Clamp in the cast- 
central part of the Annapolis quadrangle (fig. 2). The 
limestone is reddish in color and is lithologically similar 
to limestones of the Franciscan formation near Layton- 
villc and Garbcrville. It is a bed about 2 feet thick ad- 
jacent to greenstone in graj wacke and shale. Thin sec- 
tions of the limestone were examined by Professor H. E. 
Thalmann of Stanford University, who states (written 
communication, 1956) that the limestone contains micro- 
fossils that are the same as those in the limestones near 
Laytonvillc and Garberville, and that the fossils are Late 
Albian or basal Ccnomanian in age (see Irwin, 1957, p. 
2290). About \y 2 miles southwest of the YMCA Camp, 
cobble conglomerate interbedded with graywacke and 
shale is well exposed (locality no. 1, pi. 1) on the banks 
of the Gualala River, and many of the cobbles are lime- 
stone. One of the limestone cobbles contained well-pre- 
served fossils that arc identified bv R. W. Imlay (written 
communication, 1956) as Buchia piochii (Gabb) of Late 
Jurassic (middle Tithonian) age. 

Limestone at Dugans Opening, about 3'/ 2 miles north- 
east of Usal in the central part of the Piercv quadrangle 
(fig. 2) is described by Trask (1950, p. 146-147). The 
limestone appears similar to the limestone near Layton- 
villc, and occurs in about 30 lenses interbedded with sand- 
stone and greenstone within an area of less than 3 square 
miles. The limestone is lithologically similar to the lime- 
stone of the Franciscan formation at Laytonville. Most 
of the lenses are less than 5 feet thick and 20 feet in 
length, but the largest is 50 feet thick and 150 feet 
in length. The greenstones consist of flows, tuffs and in- 
trusive rocks of approximately the composition of andc- 
site. 

Near the middle of the northern half of the Porno 
quadrangle (fig. 2), thin-bedded sandstone and shale is 
well exposed along the South Fork of the Eel River at the 
mouth of Tomki Creek, and a mile farther north where 
a bridge crosses the river. At the northern locality (lo- 
cality no. 3, pi. 1) a section more than 50 feet in thickness 
is exposed. The beds strike approximately N. 30° W. and 
dip at moderate angles to the northeast. Abundant worm- 
tube structures are seen in the beds, and at a few places 
lenticular nodules of limestone arc found. In one nodule, 
a large fragment of an inoceramus was found along xvith 
a few unidentified microfossils. 

A bed of light-gray limestone in shale and graywacke 
was seen in the northeast part of the Porno quadrangle, 
at an altitude of 1,900 feet along the east side of the road 
of Laleys Ranch and about l' : miles southwest of the 
ranch. A slab of similar limestone was found in a small 
creek that drains an area of dark greenish-gray shale a 
few hundred feet south of the Old Dashiel Place in the 
northeast quarter of the Porno quadrangle. Fossils xvere 
not found at either locality. 



Cretaceous Rocks in the Klamath Mountains Province 

Small isolated patches of sedimentary strata of Creta- 
ceous age overlie the plutonic rocks and pre-Jurassic 
strata in the southern part of the Klamath Mountains 
province. They are marine deposits of sandstone, shale, 
and conglomerate that likely are remnants of a mantle 
once continuous with the strata of the Sacramento Val- 
ley. The patches arc most abundant near the Sacramento 
Valley in the Chanchclulla Peak quadrangle, where they 
obviously overlie the pre-Jurassic rocks xvith sharp angu- 
lar and erosional discordance. The patches farther north 
and northwest are widely spaced, and most are associated 
with small areas of Tertiary strata. 

The patches of Cretaceous strata at Reading Creek 
about 10 miles south of Weaverville, at Rattlesnake Creek 
in the north-central part of the Hoaglin quadrangle, and 
at Big Bar in the northeastern part of the Hyampom 
quadrangle were studied by Dillcr (1908), Hinds (1933), 
MacGinitie (1937), and Anderson (1938). At Reading 
Creek 1,000 feet of Cretaceous strata is exposed (Hinds, 
1933, p. 112), while at Big Bar the thickness is about 
200 feet (Dillcr, 1908, p. 380). The fossils found in these 
strata indicate an Early Cretaceous age (Anderson, 1938, 
p. 49-50). Most of them are of the Hautcrivian stage, 
however, Buchia crassicollis (Keyserling) of the Valan- 
ginian stage was found (U. S. G. S. Mesozoic loc. no. 
6627) at the Patterson mine near Big Bar (R. W. Imlay, 
xvritten communication, Dec. 1958). 

Se\ - eral less studied patches of Cretaceous strata occur 
in the southern part of the Klamath Mountains province. 
One is shown on the geologic map (pi. 1) 5 miles south- 
east of Hayfork, and another is on the east side of Hy- 
ampom Valley. The strata at both localities reportedly 
contain fossils of Late Cretaceous age. A small patch of 
pebble conglomerate perhaps 200 feet in width lies just 
west of a small area of Tertiary rock on the crest of the 
high ridge x\ est of Hoopa Valley, in the eastern part of 
the Coyote Peak quadrangle. The conglomerate probably 
is Cretaceous in age, but no fossils xvere found. 

A belt of Upper Cretaceous strata along the northeast 
margin of the Klamath .Mountains province north of 
Shasta Valley in California and Oregon has been de- 
scribed by F. M. Anderson (in Avcrill. 1931), Williams 
(1949, p. 16-18), and Feck. Imlay, and Popenoe (1956). 
The strata consist of buff-weathering sandstones and 
conglomerates that lie with angular unconformity on 
the plutonic rocks and pre-Jurassic strata of the Klamath 
Mountains province. The strata range widely in com- 
position, particularly the conglomerates, and reflect the 
nature of the adjacent bedrock. They constitute a section 
that is more than 2.673 feet thick (Feck, Imlay, and 
Popenoe. 1956, p. 1971). The beds dip northeastxvard at 
angles ranging between 10 and 30 degrees, and are 
thought to underlie the thin veneer of alluvium in Shasta 
Valley and perhaps continue northeastward under the 
lavas of the Cascade Range. They commonly have been 
referred to as the Chico formation, but recently (Peck, 
Imlay, and Popenoe, 1956) have been named the Horn- 



44 



California Division of Mines 



[Bull. 179 



brook formation. Anderson (in Averill, 1931) considered 
them to range from Late Turonian to Early Senonian 
in age, but according to Peck, Imlay, and Popenoe (1956, 
p. 1978-1982) the strata range at least from Cenomanian 
to middle or late Campanian in age, and include one 
unconformity. 

Uppermost Cretaceous Strata 

Three principal areas of strata of probable late Late 
Cretaceous age are shown on the geologic map (pi. 1). 
One area is chiefly in west-central Humboldt County, 
and includes the Yager formation. The second area lies 
west of the San Andreas fault from Point Arena south- 
ward to Fort Ross, and includes the Gualala series of 
Weaver (1943). The third is a small area of strata near 
Covelo in central Mendocino County. 

Yager Formation of Ogle. The Yager formation is 
the name applied by Ogle (1953, p. 16-22) to a section 
of detrital sedimentary strata typically exposed along 
Yager Creek in the Fortuna quadrangle. The total thick- 
ness of the formation is not known, but is thought to 
be more than 2,500 feet. The formation consists of inter- 
bedded shale, gravwacke, and conglomerate, with thin- 
bedded shale as the predominant rock. Specimens of 
gravwacke from five different localities contained from 
3 to 35 percent potassium feldspar, and averaged about 
15 percent. In reconnaissance mapping, the characteris- 
tics used to distinguish the Yager formation from adjacent 
rocks of the Franciscan formation and coastal belt of 
sedimentary rocks were the relative abundance of thin- 
bedded shale, the general lack of interbedded chert and 
volcanic rocks, and the relatively mild deformation of 
the Yager strata. 

As mapped, the Yager formation is nearly restricted 
to southwestern Humboldt County; small areas, however, 
may well have been overlooked at other localities in the 
Coast Ranges, particularly in the coastal belt. Conversely, 
some of the area shown as uppermost Cretaceous on the 
geologic map (pi. 1) may include detrital rock of other 
stratigraphic units. South of the area of Tertiary rocks 
in the Eel River Valley area, a westerly trending zone 
described as the False Cape shear zone by Ogle (1953, 
p. 22-24) has been included in the area shown as upper- 
most Cretaceous although other formations are reported 
to be found in that zone. 

The age of the Yager formation and its relation to the 
Franciscan formation and formations of the Sacramento 
Valley sequence is poorly known. Index fossils have not 
been found, but a small gastropod that has been found 
elsewhere in California in the Markley sandstone of 
Eocene age was noted by Ogle (1953, p. 20). Microfossils 
found in the finer-grained sediments are reported (Ogle, 
1953, p. 19) to suggest that the formation is at least as 
young as Cretaceous. Foraminifera recovered from shale 
samples collected from widespread localities during the 
present reconnaissance are chiefly agglutinated arena- 
ceous forms and are not satisfactory for age determina- 
tion. 



Ogle (1953, p. 21) assigned the Yager formation to 
the Upper Jurassic and Cretaceous, the Upper Jurassic 
assignment being based on a lithologic correlation of the 
thin-bedded shales with the Knoxville formation, and the 
Cretaceous assignment presumably being based on the 
presence of microfossils. 

Judging from the average amount of potassium feld- 
spar in the few samples that were tested, the Yager for- 
mation is as young or younger than the Upper Creta- 
ceous rocks of the Sacramento Valley sequence; and 
judging from the relatively mild deformation of many 
areas of Yager formation, it may even range into the 
Tertiary. The original extent of deposition of the Yager 
formation is not known, but its present distribution ap- 
pears to be controlled by downwarping and faulting. The 
downwarping is more clearly shown in the overlying 
late Teritary strata of the Eel River Valley area. The 
strata of the Yager formation generally dip at gentle to 
moderate angles, and over many areas have been dis- 
turbed only moderately by faulting. In contrast, the 
strata of the Franciscan formation most commonly dip at 
moderate to high angles, and have been highly sheared 
and faulted. 

The area of the Yager formation lies partly athwart 
the northwest-trending central belt of the Franciscan for- 
mation, and the Yager probably overlies the Franciscan. 
In the southwestern part of the Garberville quadrangle 
the Yager strata appear to overlie conformably the strata 
of the coastal belt, and the contact was mapped on 
the basis of relative abundance of shale and gravwacke 
(E. H. Bailey, oral communication, 1954). Northwesterly 
through central Garberville quadrangle the Yager for- 
mation is in fault contact with the Franciscan formation, 
largely along zones containing abundant serpentine. In 
the [aqua Buttes quadrangle (fig. 2) the contact between 
the Yager formation and the Franciscan rocks of the 
central belt is a fault. 

Gualala Series of Weaver. Detrital sedimentary rocks 
of the Gualala series form the narrow belt of land along 
the southwest side of the San Andreas fault between Fort 
Ross and Point Arena. They were named for exposures 
near the village of Gualala that were examined by G. F. 
Becker (White, 1885, p. 7), and were described in greater 
detail and mapped by Weaver (1943, p. 629, fig. 280). 

The Gualala series consists of interbedded gravwacke, 
shale, and conglomerate (photo 10). Samples of gray- 
wacke that were tested ranged from to 35 percent 
potassium feldspar. Pillow basalt appears to be inter- 
bedded with the detrital rocks approximately a mile 
north of Black Point in the Stewarts Point quadrangle. 
According to Weaver (1943, p. 629) the aggregate thick- 
ness of the Gualala series is 21,600 feet, but neither the 
base nor the top of the section is accurately known. 

The Gualala rocks of the report area form a north- 
westerly extension of the San Andreas-Nacimiento fault 
block of the central and southern Coast Ranges of Cali- 
fornia. They are not surely known, however, to be con- 
fined to the southwest side of the San Andreas fault. 



19601 



Northern Coast Ranges and Klamath .Mountains 



45 







-te^ 






i 









Photo 10. Gualala series exposed in wave-cut cliff at Anchor Bay, about 3 miles northwest of Gualala. 



Most of the sandstones of the Gualala series arc similar 
in hand specimen to the graywackes of the coastal belt, 
the Franciscan, and parts of the Sacramento Valley se- 
quence. Some, however, are cleaner and better sorted 
than those most commonly found northeast of the fault. 
In this respect, as well as perhaps a slightly lesser degree 
of induration, some of the sandstones more closely re- 
semble some of the Late Cretaceous formations found 
elsewhere. Conglomerates containing cobbles of quartz 
diorite occur in the Gualala series, but none was seen in 
the coastal belt northeast of the San Andreas fault. Sand- 
stone, however, similar to the cleaner sandstone most 
distinctive of the Gualala series was seen northeast of the 
San Andreas fault, about a mile southeast of lint Russ 
School along the road to Cazadero. 

The age of the Gualala series is not accurately known. 
In the vicinity of Point Arena, the Gualala is overlain b\ 
Miocene strata, but strata older than the Gualala are not 
known southwest of the San Andreas fault in the report 
area. White (1885, p. 7) considered the Gualala series to 
occupy a stratigraphic position between the Shasta series 
and the Chico formation, but Weaver (1943, p. 630) 
assigned it more broadly to the Cretaceous. If the Gua- 



lala strata arc younger than the strata generally found 
on the northeast side of the San Andreas fault, they prob- 
ably are Late Cretaceous or early Tertiary in age, as 
some of the strata on the northeast side of the fault are 
late Early Cretaceous (Late Albian) in age. According 
to Durham and Kirk (1950, p. 1537), fossils found in 
the Gualala strata indicate that some of the strata are 
probably Late Cretaceous (Maestrichtian) in age, and 
some may be Paleocenc or Eocene. 

Covelo Area. Detrital rocks of Late Cretaceous age 
that occur in several small areas southwest of Covelo in 
north-central .Mendocino County were mapped by Clark 
(1940). The rocks consist of brown- to buff- weathering 
sandstones, shales, and minor conglomerates, and are less 
well-indurated and sheared than the detrital rocks of the 
Franciscan formation of the central belt with which they 
are in fault contact. According to Clark (1940, p. 124) 
they consist of sediments derived mainly from the Fran- 
ciscan formation, and arc not lithologically distinctive 
from strata of Eocene age that are found in the same 
general area. Fossils found at several localities by Clark 
were examined by F. M. Anderson (Clark, 1940, p. 124). 
and were considered Late Cretaceous in age and younger 



46 



California Division of Mines 



[Bull. 179 



than the Chico formation. Clark states that the section 
is 4,000 feet thick, and that it is conformable with the 
overlying Eocene strata but separated by a depositional 
hiatus. 

Tertiary Rocks 

Rocks of Tertiary age occur in both the northern 
Coast Ranges and Klamath Mountains of California, and 
form a nearly continuous blanket over most of the Upper 
Jurassic and Cretaceous rocks of the Sacramento Valley. 
Included are rocks that range in age from Eocene into 
the early Quaternary. They are chiefly detrital strata, 
but volcanic rocks occur at a few widely spaced localities. 

The areas of rocks of Tertiary age in the northern 
Coast Ranges and Klamath Mountains are few in number, 
and generally are small and widely separated. The Terti- 
ary rocks of the northern Coast Ranges and the north- 
western part of the Klamath Mountains are dominantly 
marine in origin, while those of the central part of the 
Klamath Mountains are chiefly continental in origin. 

Strata of Eocene Age 

Covelo Area. Marine sedimentary strata of Eocene 
age are associated with the uppermost Cretaceous strata 
west of Covelo in north-central Mendocino County. 
Here, as elsewhere in northwestern California, several 
post-Franciscan formations occur together in a restricted 
area and have been preserved by down-faulting. 

On a paleontologic basis the Eocene strata have been 
correlated by Clark (1940) with the Martinez, A4eganos 
and Capay formations of central California. The rocks 
consist of fine- to medium-grained sandstone with minor 
interbedded shale and conglomerate. They are light 
brown to buff colored in weathered outcrops, but where 
fresh rock is exposed in deep, newly made roadcuts, the 
rock is seen to be light bluish gray in color, similar to 
most sedimentary rocks of Tertiary age elsewhere in 
northern California. The sandstones differ in this respect 
from the pre-Tertiary sandstones which generally are 
greenish and darker gray in color. In general, the Eocene 
strata in the Covelo area dip steeply northeastward. They 
were distinguished from the uppermost Cretaceous strata, 
and from each other, only on a paleontologic basis 
(Clark, 1940, p. 128). 

The strata assigned to the Martinez formation in the 
Covelo area total approximately 1 30 feet in thickness, and 
judging from the paleontologic evidence and similarity 
of structure they overlie the late Upper Cretaceous strata 
disconformably (Clark, 1940). The strata assigned to the 
Meganos formation are about 300 feet in thickness. Their 
structural attitude is similar to that of the underlying 
Martinez and overlying Capay formations. The overly- 
ing strata assigned to the Capay formation total about 
1,500 feet in thickness. 

Shasta Valley Area. Sedimentary rocks of Eocene 
age crop out in a narrow belt on the northeast flank of 
the Klamath .Mountains province. The belt trends north- 
west from the north end of Shasta Valley into southern 
Oregon, and similar rocks are thought to underlie Shasta 



Valley. The rocks have been described in most detail by 
Williams (1949), from whom much of the following 
description is taken. 

The Eocene rocks are known as the Umpqua forma- 
tion and consist of sandstone, shale, and conglomerate 
that laterally range widely in composition, and locally 
are interbedded with coal and tuffaceous material. Gen- 
erally the sandstone constitutes the lower part of the 
section, and is separated from an upper shaly part by a 
bed of coal that is a maximum of 6 feet thick. Some of 
the sandstone is seamed with limonite, and at one place 
a sandstone bed grades into a bed composed almost en- 
tirely of limonite and magnetite. The coal beds, and 
cross-bedding, and carbonized logs in some of the sand- 
stone, indicate a nonmarine origin. However, northward 
in Oregon the Umpqua formation is of marine origin. 
The thickness of the Umpqua formation ranges from 
800 to about 2,000 feet. The formation rests disconform- 
ably on the Hornbrook formation, and is overlain with 
angular discordance by Tertiary volcanic rocks. 

Strata of Oligocene(?) Age 

Several small areas of continental sedimentary deposits 
of Oligocene(P) age occur in the southern part of the 
Klamath Mountains province. The deposits were de- 
scribed by Diller (1894b, 1902, 1911, and 1914a) and 
named Weaverville formation by Hinds (1933, p. 115). 
The most detailed work, particularly with regard to a 
fossil flora found in the rocks, has been done by Mac- 
Ginitie (1937). 

The principal areas of exposure of the Weaverville for- 
mation are at Weaverville, Reading Creek, Hayfork and 
Hyampom Valleys, and Big Bar. In addition to these, 
several small patches of Tertiary deposits that are pos- 
sibly related were found during the present reconnais- 
sance at Corral Bottom, Clark Creek, and Buckhorn 
Creek in the northern part of the Hyampom quadrangle 
(fig. 2), and northwest of Hoopa Valley. 

The areas of Weaverville formation are small blocks 
that have been preserved by being faulted into the older 
rocks of the southern part of the Klamath Mountains 
province. At several of these areas of Tertiary rocks, 
small areas of strata that range from Early to Late Cre- 
taceous in age are similarly preserved, as at Reading 
Creek, Big Bar, Hvampom Valley and possibly at Hoopa 
Valley. 

The Weaverville formation consists of fine-grained 
sandstone, shaly sandstone, sandy shale, fine-grained lake 
beds, lignitic shale, lignite, tuff, and conglomerate (Hinds, 
1933, p. 115), that are thought to have been deposited 
on a flood-plain with widespread swampy lakes (Mac- 
Ginitie, 1937, p. 102). Some may be estuarine (Diller, 
1902, p. 43). The lignite has been mined on a small scale 
at several localities (photo 11). At Hyampom Valley a 
lignite bed ranges from 10 to 16 feet in thickness (Mac- 
Ginitie, 1937, p. 96). A thick section of lignite is well 
exposed on the northeast bank of the South Fork of 
the Trinity River, where a bridge on the county road 
spans the river about one-quarter mile west of Hyampom. 



1960| 



Northern Coast Ranges vnd Kj vmath Mot ntains 



47 












^' ? 



Photo 11. Lignite inte 
coal 



roedded with light colored clay, siltstone, and sandstone of the Weaverville formation at Reese Brothers 
mine, near Browns Creek in the central p.irt of the Weaverville 15-minute quadrangle. 



I he Weaverville strata at m:>st places ilip gently to mod- 
erately, lint at a few localities where they are in fault 
contact with adjacent older rocks they dip steeply. The 
thickness of the Weaverville formation is 1,900 feet at 
Reading (.'reek, probably not less than 2,000 feet at Hay- 
fork Valley, and about 1,100 feet at Hyampom; ar J5ig 
Bar it is a little less than 500 feet but neither the top nor 
the bottom of the section is exposed (MacGinitie, 1937). 
\n abundant fossil flora is found in some of the shaly 
beds of the Weaverville formation. The flora was first 
considered to indicate a Miocene age (I)iller, 1902, p. 41- 
45), and later thought to be chiefly Eocene (Hinds, 1933, 
p. 79, 114-116; Jenkins, 1938). According to MacGinitie 
(1937, p. 129), however, the flora is Oligocene in age. 

The Weaverville formation was considered by Dillcr 
I 1902, p. 12) to be associated with the development of 
the Sherwood peneplain, that is, the so-called second 
cycle of erosion. If MacGinitie's (1937) assignment of 
the formation to the Oligocene is correct, however, the 
\\ eavcrvillc formation is older than even Diller's Klamath 
peneplain. 

Strata of Miocene Age 

Marine sedimentary deposits of Miocene age occur at 
Point Arena, and near Covelo, Garberville, Petrolia, and 
along the Bear River. Deposits in western Del Norte 
County that commonly are referred to as Miocene in age 
are discussed with strata of Pliocene age in this report. 

Point Arena Area. At Point Arena, along the coast 
of southern Mendocino County, marine sedimentary de- 
posits are exposed over an area of about 1 1 square miles, 
and constitute the largest area of exposure of Miocene 
rocks in northwestern California. Thev have been 



mapped and described by Weaver ( 1943, p. 630-631, and 
fig. 280), who separated the strata into lower and upper 
units. 

The lower unit, the Gallaway beds, consists of dark- 
gray and brown argillaceous shale, mudstone and me- 
dium-grained sandstone, interlaycrcd with thick beds of 
brownish-gray sandy shales and foraminiferal shales. The 
upper unit, the Point Arena beds, consists of interbedded 
gray-brown clay shales, diatomaceous and foraminiferal 
shales, and cherty shales. Sandstone beds nearly 50 feet 
thick occur at intervals in the upper unit, and two of 
these contain abundant petroleum residues. Some vul- 
canic ash is found in the upper unit. The Miocene age of 
the strata is based on study of the foraminiferal fauna. 

The Gallaway beds are 2,075 feet thick, and the Point 
Arena beds are 3,355 feet thick. They have been folded 
moderately into several small anticlines and synclincs that 
trend northwest, parallel to the San Andreas fault, and 
rest with angular unconformity on the strata of the 
Gualala series. The folded Miocene strata are beveled 
(photo 12), and are overlain with marked angular uncon- 
formity by marine sedimentary deposits of Pleistocene 
age. 

Covelo Area. Several small areas of sedimentary de- 
posits of Miocene age occur west of Covelo near small 
areas of rocks of late Late Cretaceous and Eocene age. 
Thev occur in separate fault blocks, however, and with 
the exception of one place where they are in fault contact 
with strata of late Late Cretaceous age, they are every- 
where in fault contact with rocks of the Franciscan for- 
mation. The deposits have been described by Clark (1940, 
p. 131-138), who correlated them with the Temblor 
formation (middle Miocene) of central California. 



48 



California Division of Mines 



(Bull. 179 




Photo 12. Anticline in strata of Miocene age, near Point Arena. 



The strata of Miocene age consist mainly of sandstone 
and conglomerate, with some interbedded shale and a 
few beds of coal. Conglomerate is much more abundant 
than in the nearby areas of older Tertiary strata. Some of 
the coal has been mined on a small scale. In general the 
strata dip gently northeastward, and attain a thickness of 
more than 2,200 feet. A marine molluscan fauna of 
Miocene age is fairly abundant. According to Clark 
(1940, p. 134) the source of the sediment was partly 
the Franciscan group, and he interprets the strata to have 
been deposited under shallow-water, near-shore marine 
or estuarine conditions. 

Garberville Area. Marine deposits of Miocene and 
Pliocene age have been mapped as two elongate areas 
near Garberville by MacGinitie ( 1943, fig. 282) and 
Bailey (see pi. 1 ), and one near Piercv. Those of Miocene 
age have not been differentiated on the map (pi. 1) from 
the associated deposits of Pliocene age, but according to 
E. H. Bailey (oral communication, 1954) the Miocene 
deposits occur principally in the western of the two 
areas near Garberville. The strata of Miocene age consist 
of diatomaceous mudstone with interbeds of medium- 
grained sandstone, and are 900 to 1,200 feet thick. Ac- 
cording to MacGinitie they are correlative with the Santa 
Margarita formation of Late Miocene age (1943, p. 633). 
The Tertiary rocks of the Garberville area have been 
warped into northwest-trending synclines, and are in 
contact with rocks of the Franciscan formation and 
Yager formation along northwest-trending faults. The 
relation between the Miocene and Pliocene rocks is not 
known. 

Petrolia Area. Limestone float containing megafossils 
was found (locality no. 10, pi. 1; U. S. G. S. Cenozoic 
loc. no. 19054) at the mouth of LaRue Gulch in W'/ 2 
sec. 6, T. 2 S., R. 2 W., about 3% miles west of Petrolia. 
The fossils were examined by the late Ralph Stewart and 
E. J. Trumbull of the U. S. Geological Survey who re- 
ported as follows: 



"Gastropods: 

Bathybembix? sp. cf. B.? Washingtoniana (Dall) 

Amauropsis? sp. cf. A. oregonensis (Dall) 
"Pelecypod: 

Volsella sp. V. cf. modiolus (Linne) 

"The gastropods were both originally described from the Em- 
pire formation (Pliocene?) at Coos Bay, Oregon. Volsella modi- 
olus is a circumboreal bivalve which has been found living as far 
south as San Pedro (Dall, W. H., 1921, U. S. Nat. Mus. Bull. 112, 
p. 21 as Modiolus modiolus). 

"Age: Miocene or Pliocene (?): No positive age determina- 
tion could be made on the basis of the fossils submitted. The 
fauna may belong to the Wildcat formation and may be in- 
dicative of a moderately deep-water (5-50 fathoms) environ- 
ment." 

Winter Formation of Maxson (1933). A few small, 
thin, patches of marine sediments occur at an altitude of 
approximately 2,000 feet on the western margin of the 
Klamath Mountains province in western Del Norte 
County. They occur at the general level of a dissected 
old-land surface, the Klamath peneplain, and are consid- 
ered by Diller (1902, p. 30, 32) to have been deposited 
during development of the Klamath peneplain. The rocks 
were named Wymer beds by Diller (1902, p. 32-33), 
and have since been re-named Wimer formation by Max- 
son (1933, p. 134, see Wilmarth, 1938, p. 2347). The 
formation consists of friable shales, sandstones and con- 
glomerates that weather yellowish and reddish in color. 
Maxson states that the beds are flat-lying and that the 
formation is a maximum of 150 feet in thickness (1933, 
p. 134). Imprints of mollusks and plants are abundant 
locally in the beds, and according to F. H. Knowlton 
(in Diller, 1902, p. 33) and Maxson (1933, p. 135) the 
fossils indicate that the deposits are late Aliocene in age. 
Diller considered the Wymer beds to be eastern ero- 
sional remnants of marine deposits exposed 10 to 15 
miles westward at Point St. George (1902, p. 32); how- 
ever, the beds at Point St. George are now thought to 
be Pliocene in age (Allen and Baldwin, 1944). 



I960] 



Northern Coast Ranges and Klamath Mountains 



49 



In the Gasquet quadrangle. Cater and Wells (1954, 
p. 104-105) describe deposits of gravel that occur only 
at the same general altitude as the Wimer formation, and 
that till channels that have been cur into the Wimer and 
older formations. The gravels are poorly sorted, and 
include clay as well as boulders. Some of the pebbles and 
boulders arc fresh and hard, while others arc thoroughly 
weathered and crumble easily. Cater and Wells (1954) 
believe the gravels to have been deposited shortly after 
emergence of the Wimer formation, and that the gravels 
probably are late Miocene or early Pliocene in age. 

Gravels that arc similar to those described by Cater and 
Wells ( 1954) occur for 2 l / 2 miles along the broad crest 
of French Camp Ridge, about 8 miles northwest of 
Hoopa Valley, and at an altitude of approximately 3,000 
feet. They are poorly sorted anil contain both fresh and 
thoroughly weathered cobbles. Diller (1902, p. 52-54) 
considered these gravels to have been deposited in an 
ancient bed of the Klamath River. 

Strata of Pliocene Age 

Marine sedimentary deposits of Pliocene age are widely 
distributed in the northern Coast Ranges, and form the 
greatest total area of exposure of Tertiary rocks. None 
is found in the Klamath Mountains province except for a 
few small patches along the extreme western margin in 
western Del Norte Count). Continental deposits of Plio- 
cene age, principally the Tehama formation, are wide- 
spread along the west side of Sacramento Valley, but as 
they are somewhat beyond the scope of this report the 
reader is referred to Anderson and Russell ( 1940). 

Southern Coastal Area. In southwestern Mendocino 
and northwestern Sonoma Counties, marine scdimentar\ 
deposits of Pliocene age (Peck, 1957) occur in a north- 
west-trending belt about 20 miles long and 4 miles wide 
along the east side of the San Andreas fault. C. G. Hig- 
gins has mapped these deposits (data incorporated in 
geologic map, pi. I) and described them (Higgins, 1957). 
The outcrops are erosional remnants of a formerly con- 
tinuous blanket that overlay much of the coastal belt 
of undivided sedimentary rocks with high angular un- 
conformity, and that has since been dissected by the 
South Fork of Ciualala River and its tributaries. The 
Pliocene strata consist dominantly of weakly consoli- 
dated, light-colored sandstones, with some conglomeratic 
and finer grained sediments, and a few thin layers of 
white tuff. The strata are as much as 200 feet in thick- 
ness, and have been only mildly warped and faulted. 
They appear to have been deposited on a shallow sub- 
marine terrace, and have since been uplifted to altitudes 
ranging from 500 to 1,700 feet above sea level (Higgins, 
1957). A fossil molluscan fauna of Pliocene age indicates 
that the deposits are equivalent in age to the lowermost 
Merced formation of the San Francisco Peninsula or the 
upper Purisima formation of the Santa Cruz quadrangle 
(Peck, 1957). 

Wildcat Group of Ogle (1951). The name Wildcat 
series was given by Lawson (1894) to marine sedimen- 



tary deposits of Tertiary age in the Eel River Valley 
area of western Humboldt County. Ogle (1951) called 
it the Wildcat group. The deposits have been studied 
by manv geologists, and for a review ol the previous 
literature the reader is referred to Stewart and Stewart 
( 1949, p. 174-185). The deposits were mapped and de- 
scribed in derail by Ogle (1953). 

Ogle's Wildcat group consists of weakly consolidated 
mudstone, siltstone, sandstone and conglomerate, and 
minor intcrbeds of limestone, tuff, and lignite. In the 
southern parr of the Fel River Valley area, the group 
has been subdivided into five formational units by Ogle 
(1953, p. 26-39), from oldest to youngest, the Pullen, 
Eel River, Rio Del, Scotia Bluffs and Carlotta formations. 
The three oldest formations consist dominantly of fine- 
grained sediments, whereas the two youngest formations 
consist dominantly of coarse-grained clastic sediments. 

In the Eel River Valley area the Wildcat strata arc a 
total of 12,000 feet thick. They dip gently to moderately, 
and in over-all view the structure is thought to be a 
broad syncline whose axis trends west-northwest. Minor 
anticlines on the limbs of the syncline plunge westerly 
(Ogle, 1953, p. 64). The base of the Wildcat group has 
not been seen, but it is thought to rest with marked 
angular unconformity on the Yager formation (Ogle, 
1953, p. 26). 

Abundant fossils of a molluscan and foraminifcral 
fauna indicate the Wildcat group to be dominantly ma- 
rine deposits of Pliocene age. However, the oldest unit, 
the Pullen formation, may range in age to Late Miocene 
(Mohnian), and the youngest unit, the Carlotta forma- 
tion, is dominantly non-marine and may be as young as 
early Pleistocene (Ogle, 1953, p. 28, 38). 

The Wildcat group likely is of considerable submarine 
extent west of the Humboldt Bay area, judging from the 
westward ami northwestward structural trends of the 
formation and the bounding faults, and from the results 
of dredging off the coast. Hanna (1952, p. 333, 342, and 
358, fig. 2) reports that numerous fragments of Wildcat 
strata containing fossils were dredged from depths of 
80 to 120 fathoms as far as 30 miles out to sea west of 
Humboldt Bay, and that similar fossiliferous rocks w ere 
found southwest of Trinidad Head at 96 fathoms. It 
should be noted, however, that the 30-mile distance ap- 
pears erroneous, as the continental slope at a distance of 
30 miles offshore from Humboldt Bay is at depths rang- 
ing from 400 to more than 1.00(1 fathoms according to 
the map of California, editon of 1953, U. S. Geological 
Survey. Depths of 120 fathoms or less appear to be no 
further than approximately 12 miles offshore from Hum- 
boldt Bay. 

During the present reconnaissance, mapping of the 
Eel River Valley area of the Wildcat group was extended 
southeastward into the Weott quadrangle (fig. 2). In 
addition, four small areas of Tertiary rocks that likely 
are correlative with the Wildcat group were found. Two 
of these arc in the Weott quadrangle. The other two are 
along the boundary between the Alderpoint and Hoaglin 



50 



California Division of .Mines 



[Bull. 179 



quadrangles, but are too small to be shown on the geo- 
logic map (pi. 1 ). 

In the extended area of the Wildcat group fossils were 
collected (locality no. 14, pi. 1; U. S. G. S. Cenozoic 
loc. no. 19053) along Highway U. S. 101 in NW14 
sec. 32, T. 1 N., R. 2 E., about l'/ 2 miles south of Pep- 
perwood in the northwestern part of the Weott quad- 
rangle. The fossils are from moderately dipping, friable 
mudstone that is thought to be of the Wildcat group. 
They were studied by E. J. Trumbull of the U. S. Geo- 
logical Survey, who reports as follows: 

"Gastropods: 
Ncptunea? sp. 
Gyrineum sp. cf. G. scotiaensis (Martin) 

"Pelecypod: 
Yoldia? sp. 

"Age: Pliocene (?). No positive age determination could be 
made on the basis of the fossils submitted. The fauna may 
belong to the Wildcat formation and may be indicative of a 
moderately deep-water (5-50 fathoms) environment." 

In the northeastern part of the Weott quadrangle, 
Tertiary sediments are exposed over an area of half a 
square mile along the county road between Bridgeville 
and Blocksburg in W'/ 2 sec. 30, T. 1 N., R. 4 E., and 
E'A sec. 25, T. 1 N., R. 3 W. The rocks are dominantly 
friable, medium-grained sandstones that are light bluish 
gray in color where unweathered. Fossils are abundant 
near the eastern limit of the area. Specimens collected 
from that locality (locality no. 15, pi. 1; U. S. G. S. 
Cenozoic loc. no. 19052) were studied by E. J. Trumbull, 
who reports as follows: 

"Gastropods: 

Cryptonatica sp. cf. C. clausa (Broderip and Sowerby) 
Unidentified naticids 
Nassarius? sp. 

"Pelecypods: 

Crvptomva? sp. cf. C. californica (Conrad) 

Volselh?'sp. 

Macoma? sp. cf. M. nasuta (Conrad) 

Chione (Securella) securis (Shumard) 

Solen? sp. 

Unidentified pelecypod 

"Age: Pliocene (?). No positive age determination could be 
made on the basis of the fossils submitted, but they may 
belong to the Wildcat formation and may indicate a moder- 
ately shallow-water (less than 5 fathoms) environment." 

The other small area of Tertiary rocks in the Weott 
quadrangle covers about a square mile on the northeast 
side of the Eel River east of AlcCann. It consists of mud- 
stone, sandstone and conglomerate, much of which has 
been sheared. The Tertiary rocks are surrounded by the 
Yager formation, and the contacts between the two seem 
likely to be faults. Fossils in pebblv sandstone collected 
in SE'/4NW l / 4 sec. 3, T. 2 S., R. 3 E. (locality no. 11, 
pi. 1; U. S. G. S. Cenozoic loc. no. 19051) were studied 
by E. J. Trumbull, who reports the following: 

"Gastropods: 
Calliostoma? sp. 
Unidentified trochid 
Unidentified calyptrid 
Thais? sp. 
Unidentified gastropod 



"Scaphopod: 

Ucntalium sp. 

"Pelecypods: 

Patinopecten? sp. 
Vertipecten? sp. 
Unidentified cardid 

"Age: Pliocene? No positive age determination could be made 
on the basis of the fossils submitted. The fauna may belong 
to the Wildcat formation, and may be indicative of a moder- 
ately deep-water (5-50 fathoms) environment." 

One of the two localities of Tertiary rock along the 
boundary between the Hoaglin and Alderpoint quad- 
rangles is approximately in EVz sec. 4, T. 4 S., R. 6 E., 
on the road from Kettenpom Peak to Blocksburg Ranger 
Station. The general area is one of highly sheared rocks 
of the Franciscan formation and small bodies of serpen- 
tinized ultramafic rock. The Tertiary rocks are exposed 
discontinuously in shallow road cuts for about 400 feet. 
They consist chiefly of weakly consolidated sandstones 
and conglomerate. The sandstones are light-buff where 
weathered, but are light-cream or pale bluish-gray where 
fresh. Bedding is obscure, but the strata appear to dip 
about 45 degrees to the southeast. Fossils were not found, 
but in general comparison with rocks seen elsewhere, the 
strata seem likely to be of Pliocene age. 

The other locality is about 4 miles north of the previ- 
ously described locality, and is along the road between 
Zenia and Alderpoint. It consists of several isolated areas 
of Tertiary strata that are exposed for widths of a few 
hundred feet at intervals between points 54 to 1 mile 
southwest of Zenia. The areas of Tertiary rocks appear 
to be fault blocks in a general area of sheared rocks of 
the Franciscan formation, and at one place the contact 
between the two is a nearly vertical fault. The Tertiary 
rocks consist of friable mudstone, sandstone and con- 
glomerate. The sandstones generally are light-buff where 
weathered, but pale bluish-gray or greenish-gray where 
fresh. The beds dip at low to moderate angles, generally 
eastward. Abundant fossil mollusks were seen at one 
exposure but were too poorly preserved to be specifi- 
cally identified. The fine-grained sediments (locality no. 
12, pi. 1) contain radiolaria, sponge spicules, and diatoms 
of Pliocene age, similar to those found in samples from 
the Wildcat group in the northwestern part of the Weott 
quadrangle. 

Falor Formation of Manning and Ogle (1950). In the 
Blue Lake quadrangle (fig. 2) along the lower reaches 
of the Mad River, Tertiary rocks occur as a northwest- 
trending fault block in Franciscan rocks. The Tertiary 
rocks have been described as the Falor formation by 
Manning and Ogle (1950, p. 22-25), and are thought to 
be equivalent to part of Ogle's Wildcat group. They are 
chiefly marine detrital deposits, consisting mostly of 
gray- to buff-colored sandstone, shale and conglomerate, 
with a few interbeds of limestone and lignite. The strata 
range from 750 feet thick near Korbel, to 2,460 feet thick 
elsewhere. The upper 200 feet of the section near Korbel 
consists of red-brown clays and gravels that may be 
continental deposits. The beds of the Falor formation 



1960] 



Northern Coasi Ranges and Klamath Mountains 



51 



dip about 20 degrees northeast. Fossil mollusks are 
abundant locally, and the) indicate the formation prob- 
ably is upper lower Pliocene and extends into lower 
middle Pliocene (Manning and Ogle, L950, p. 20-23). 
The detrital sediments are thought to have been derived 
from areas of the Franciscan formation and Kerr Ranch 
schist nearby. 

St. George Formation. In western Del Norte County, 
marine sedimentary deposits of Tertiary age were de- 
scribed by Oilier (1902, p. 31-35) as the Point St. George 
beds and the Crescent ( itv beds. They have since been 
included under the name St. George formation by 
Maxson (1933, p. 135). 

The St. George formation is exposed in a few small 
areas along the coast in the vicinity of Point St. George 
and Crescent City. It probably underlies much of the 
low, broad coastal terrace at the mouth of the Smith 
River, but is concealed by a thin veneer of Pleistocene 
and Recent deposits. The formation consists of weakly 
consolidated marine deposits, chiefly light gray and buff- 
colored sandstones and shales. The beds dip northeast- 
ward at low to moderate angles. A thickness of about 
100 feet of the strata are exposed, but the maximum 
thickness of the formation is thought to be considerably 
greater (Maxson, 1933, p. 135). 

Some of the beds are abundantly fossiliferous. Oilier 
(1902, p. 32) considered the Point St. George beds to 
be Miocene in age and correlative with the Fmpire for- 
mation of coastal Oregon, based on faunal studies by 
W. II. Oall (in Oilier, 1902). On the same basis the 
Crescent City beds were thought to be largely Miocene, 
but in part Pliocene in age. The Empire formation has 
since been called Pliocene in age (Allen and Baldwin, 
1944, p. 29-31), and on this basis the St. George forma- 
tion seems likely to be of Pliocene age as designated by 
Maxson (1933, p. 135). 

Cache Formation of Anderson (1936). Lacustrine 
and fluvial deposits crop out over an area of approxi- 
mately 40 square miles in the Coast Ranges east of Clear 
Lake. They were first described by Becker (1888, p. 219) 
as the Cache Lake beds, but later were renamed the 
Cache formation by Anderson ( 1936, p. 633). The de- 
posits are not thought to represent a former extension 
of present-day Clear Lake ( Anderson, 1936, p. 638). The 
most detailed studies of the Cache formation have been 
by Anderson (1938, p. 632-639) and Brice (1953, p. 
30-34), and the following description is chiefly a sum- 
mary of their work. 

The Cache formation consists of a thick series of beds 
of weakly consolidated gravels, sands and silts. Some 
of the beds are calcareous, and thin beds of tuff arc found 
locally. Layers of basalt that form conspicuous tablelands 
in the area are considered to be interbedded with sedi- 
mentary rocks of the upper part of the Cache formation. 

The formation is remarkably thick, considering its 
mode of origin and seemingly small basin of deposition. 
Anderson (1936, p. 633) estimates a maximum thickness 



of at least 1,700 feet. Brice < 1953, p. 33) estimates a maxi- 
mum thickness of 6,500 feet, and states that at some 
localities he presumes to be near the edges of the basin of 
deposition, the formation is only a few hundred feet 
thick. Anderson (1936, p. 638) states that "the surface 
on which the Cache formation accumulated must have 
had considerable relief, judging from the marked differ- 
ences in thickness of the rocks underneath the inter- 
bedded basalt flow . . . ", thicknesses ranging from 100 
feet to at least 1,700 feet. 

1 he strata of the Cache formation have been folded 
mildly and generally dip at angles of less than 25 degrees. 
Within the map area the formation may be entirely in 
fault contact with older rocks, but nearby to the south 
it lies with marked angular unconformity on rocks of 
Eocene and older ages. Subsequent to folding and fault- 
ing, the formation was overlain by Recent lava flows 
in the map area, and by volcanic rocks of Pleistocene age 
in areas near Lower Lake to the south. 

The age of the formation is not accurately known. In- 
conclusive evidence of a late Pliocene or early Pleistocene 
age, based on freshwater invertebrate and fragmentary 
vertebrate fossils, has been summarized by Anderson 
(1936, p. 639). He tentatively regards the Cache forma- 
tion as early Pleistocene in age, but notes the marked 
lithologic similarity to the Tehama formation of late 
Pliocene age (Anderson, 1936, p. 639). The nearest ex- 
posures of the Tehama formation are in the Sacramento 
Valley approximately 10 miles east of the Cache for- 
mation. 

Volcanic Rocks of Tertiary Age 

Few areas of volcanic rocks of Tertiary age, other 
than those previously mentioned in association with 
chiefly sedimentary formations of Tertiary age, are found 
in the portion of the northern Coast Ranges and Klamath 
Mountains shown on the geologic map (pi. 1). In ad- 
jacent areas, however, volcanic rocks of 1 erriary age are 
relatively abundant. Some of these, principally the rocks 
of the Cascade Range east of Shasta Valley, are shown 
on the geologic map (pi. 1) as a matter of convenience 
in outlining the report area; they will not be described in 
detail. 

Basalt crops out in a small wedge-shaped area at the 
coast a few miles south of Point Arena, at the contact 
between the Gualala series and the Gallaway beds. The 
basalt has been mapped, and named Skooner Gulch basalt 
by Weaver (1943, p. 629-630, fig. 280). As described 
by Weaver, the basalt is 900 feet thick. Some of it shows 
flow and pillow structures, and some contains lens-like 
masses of tuffaceous sandstone. He interprets the basalt 
to be a submarine flow that lies unconformably on de- 
formed strata of the Gualala series, and as older than the 
adjacent. Gallaway beds. It is not clear whether Weaver 
(1943, compare the stratigraphic column, p. 630, with 
fig. 280, p. 631) considered the basalt to be entirely Ter- 
tiary in age or in part Cretaceous in age. If the strati- 
graphic relations described by Weaver are correct, and 
if, as suggested by Durham and Kirk (1950, p. 1537), 



52 



California Division of Mines 



[Bull. 179 



the Gualala series is in part as young as Eocene, all of 
the Skooner Gulch basalt must be Tertiary in age. 

Volcanic rocks crop out approximately 1,000 feet 
along Rockpile Road in a general area of Franciscan 
rocks in the north-central part of the Skaggs Spring 
quadrangle, in E'/ 2 sec. 10, T. 10 N., R. 11 W. The area 
is too small to be shown on the geologic map (pi. 1). 
The rock is chiefly basalt with vesicles and pillow struc- 
ture, and may be an isolated remnant of the Sonoma 
group (Dickerson, 1922) of late Pliocene age. The 
Sonoma group has not been found north or west of this 
locality, but beyond the map area, to the east in the 
Healdsburg quadrangle (Gealey, 1951), and to the south- 
east nearly to San Francisco Bay (Weaver, 1949, and 
others), it covers large parts of Sonoma and Napa 
Counties. 

Quaternary Rocks 

Sedimentary and volcanic rocks of Quaternary age 
cover only a small percent of the northern Coast Ranges 
and Klamath Mountains area, although deposits of similar 
age are extensive in the provinces adjacent to the east. 
The older rocks, of Pleistocene age, are marine and con- 
tinental in origin and are chiefly exposed in terraces. The 
younger rocks, of Recent age, are continental in origin 
except for small areas of beach and dune sands along the 
coast. Volcanic rocks of both Pleistocene and Recent 
ages are prominent near Clear Lake in the northern Coast 
Ranges, but none are found in the Klamath Mountains. 
The pattern of distribution of the rocks of various origin 
indicates that the general configuration of the coastline 
has changed little since early Quaternary time. 

Marine Sedimentary Deposits. Marine deposits of sand 
and gravel of Pleistocene age occur in a narrow belt along 
the coast as a thin capping on wave-cut terraces. Since 
their deposition they have been elevated far above 
present-dav sea level and have been dissected deeply by 
Recent streams. Many of the remnants of these deposits 
are too small to be shown on the geologic map (pi. 1 ). 
The terraces occur at several different altitudes and 
usually are less than 3 miles distant from the coast. Along 
the coast of Sonoma and Mendocino Counties the terrace 
deposits appear to occur chiefly within two ranges in alti- 
tude, from 50 to 100 feet, and from 250 to 500 feet. East 
of the narrow belt of terrace gravels prominent flat sur- 
faces were seen on many of the principal ridges, mainly 
at altitudes ranging approximately from 1,000 to 2,000 
feet, but these appeared generally devoid of Quaternary 
deposits. Lawson (1894, p. 246-247), however, studied 
the terraces in the vicinity of Fort Ross at the south end 
of the map area (pi. 1) in some detail; he states that wave- 
cut terraces occur at altitudes of 280, 350, 760, 1,1 SO, and 
1,400 feet. The highest terrace on which he found evi- 
dence of wave action is 2 ! A miles east of Fort Ross at an 
altitude of 1,520 feet. Beach sands and gravels also were 
found at some of the highest of these altitudes. Lawson 
(1894, p. 246) considered a flat-topped ridge at an alti- 
tude of 1,600 feet east of Fort Ross, to be an erosional 



remnant of a widespread coastal plateau. The age rela- 
tions are not clear among the higher terrace deposits, the 
so-called plateau surfaces, and the mildly deformed 
blanket of marine sedimentary rocks of Pliocene age 
described by Higgins (1957). 

Further north, near the mouth of the Fel River, marine 
terrace gravels are found at an altitude of 900 feet, and 
may be equivalent in age to the Hookton formation; 
other terraces are numerous in the area, but they are 
capped by floodplain deposits of the Rohnerville and 
Hookton formations of Pleistocene age (Ogle, 1953, p. 
63-64). 

The broad coastal plain in the vicinity of Cresent City 
is at an altitude of about 50 feet. It is an emerged marine 
terrace that appears to have been cut chiefly on deformed 
rocks of the St. George formation of Pliocene age. It is 
overlain by a thin veneer of the Battery formation (Max- 
son, 1933, p. 136), by beach and dune sands, and by 
alluvial debris from the Smith River. The Battery forma- 
tion consists of unconsolidated strata of Pleistocene age 
that are exposed on the southern part of the terrace. 
Olmsted (1956, p. 20-21) states that the formation con- 
sists of ". . . fine sand, silt and clay, and a basal 1-foot 
bed of pebble gravel. The thickness of the Battery aver- 
ages about 35 feet but locally is as much as 60 feet." 

Recent deposits of beach and dune sand are sparse. 
Most of the rugged coastline is faced by steep cliffs, and 
the beaches that fringe the cliffs arc narrow and short. 
Beach sands and associated dune sands are most abundant 
near the mouths of the principal rivers. Some of these 
deposits are of minor economic interest as a source for 
special purpose sands, for their heavy-mineral content 
such as chromite (Wells, Cater, and Rynearson, 1946, 
p. 74-76) and, to a lesser degree, gold and platinum 
(Maxson, 1933, p. 143) along the coast of Del Norte 
and northern Humboldt Counties. 

Continental Sedimentary Deposits. Fluvial and la- 
custrine deposits that range from Pleistocene to Recent 
in age occur chiefly in the few broad intermountain val- 
levs and along the coast of northern Humboldt County 
near the mouths of the Eel and Mad Rivers and Red- 
wood Creek. The older deposits are very mildly de- 
formed, and are exposed chiefly in terraces that have 
been cut by recent streams. They have been studied in 
most detail by Ogle (1953, p. 57-63) near the mouth 
of the Eel River where they are known as the Rohner- 
ville and Hookton fotmations. Fluvial deposits occur also 
on relatively small terraces that are perched along the 
courses of the major streams, at elevations ranging from 
a few feet to several hundred feet above the present 
streams. They are broadly correlative in age with the 
fluvial deposits of the intermountain valleys and coastal 
areas. Along the upper reaches of the Trinity River they 
include the auriferous gravels that have been referred 
to as gravels of the third cycle by Diller (1911, p. 26-28). 
Recent deposits of sand and gravel are sparse along many 
of the upper reaches of the streams, however, owing to 
the rampageous discharge and flushing action of the 



19601 




Northern Coasi Ranges vnd Klamath Mountains 



S3 




' i 



V 



', • 



. > 



A * 






.' j ■,< t t y ■■-{-■ \f /./. 



Www* W-Mmik n h\ , s 



i j ( 



PHOTO 15. Strata of Pleistocene age exposed m .1 road cut on Route 2u cast of Calpclla. 1 he str.ir.i consist of silr, sandstone, .unl 
conglomerate, and dip 1_ NW. Note the erosional disconformity between the conglomerate and beds of silt and sandstone. 



streams during the rainy season. Glacial deposits have 

been found in some parts of the Klamath .Mountains, and 
to a smaller extent in the northern ("oast Ranges. 

The 1 lookton formation, as described by Ogle (1953, 
p. 57-63), consists of orange- or yellow-brown colored 
gravel, sand, silt, and clay, and may be as thick as 420 
feet. The rocks arc mainly nonmarine, hut some may be 
cstuarine. The Rohnerville formation is similar in color 
to the Hookton, hut is mainly floodplain gravels and 
ranges from 10 to only 2> feet in thickness. Both forma- 
tions were deposited unconformably on the Wildcat 
group of Pliocene and earl) Pleistocene (?) age. The 
Hookton formation probably is middle and late Pleisto- 
cene. The Rohnerville formation is thought to be late 
Pleistocene, but younger in age than the Hookton. Both 
formations have been gently folded along the old struc- 
tural axes of the more highly deformed Wildcat group. 
Similar deposits near the mouth of Redwood Creek in 



the central part of the Orick quadrangle (fig. 2) have 
been mentioned by Rice ( 1953, p. 2779). 

The principal intermountain valleys that arc filled 
with appreciable quantities of sedimentary rocks of 
Quaternary age are in the northern Coast Ranges. The 
older of these rocks are herein considered to be of prob- 
able Pleistocene age, as they are exposed chiefly in high 
terraces, are weakly consolidated, and are mildly de- 
formed and faulted. However, fossils diagnostic of their 
age have not been found, and the possibility of a late 
Pliocene age for some of the rocks should not be dis- 
regarded. The strata consist mainly of gravel and sand, 
but include silt and clay, and appear to he fluvial and 
lacustrine' in origin (see Davis, 1933, p. 195). The higher 
terrace deposits generally arc remnants of a formerly 
more extensive and deeper valley fill. 

Along the Russian River, east of Ukiah, and between 
the East Fork of the Russian River and Redwood Valley 



54 



California Division of Mines 



[Bull. 179 



east of Calpella (photo 13), the principal high terrace 
underlain by deposits of Quaternary age is at an altitude 
of 1,000 feet above sea level, and has been entrenched to 
a depth of about 400 feet. Deposits in Potter Valley are 
at a similar altitude but are entrenched less deeply. In- 
vestigations of the Coyote Dam site on the East Fork of 
the Russian River indicate the older valley fill to have 
been 1,000 feet thick (Treasher, 1955, p. 1666), that is, 
the old valley floor is 1,000 feet below the terrace level. 
The old valley floor must therefore be about at present- 
day sea level. 

Southeast of Willits in Little Lake Valley a thickness 
of more than 200 feet of sediments is exposed between 
the valley floor and the terrace level at an altitude of 
about 1,700 feet. According to Olmsted (1956, p. 86-87) 
the deposits that underlie the terrace consist of clay, 
diatomaceous shale, silt, sand, gravel, and conglomerate, 
with an estimated thickness of several thousand feet. The 
south end of Round Valley, near Covelo, has been cut 
to a depth of about 200 feet in mildly deformed beds of 
gravel, sand, and clay that are exposed at an altitude 
similar to those of Little Lake Valley, and the total depth 
of the valley fill is estimated by Olmsted (1956, p. 83) 
to exceed 1,000 feet. 

A widespread terrace at a general altitude of 1,500 feet 
along the west side of Clear Lake is underlain by uncon- 
solidated sands and gravels. The terrace level is about 200 
feet higher than the recent valley fill and artificial level 
of Clear Lake. Nearby, about 4 miles southwest of Kel- 
seyville, deformed beds of weakly consolidated fine- 
grained sediments underlie a somewhat higher old-land 
surface, and may be older than the sediments that underlie 
the 1,500-foot terrace. An ancient valley surface appears 
to have developed at an altitude of about 2,300 feet in the 
vicinity of Lake Pillsbury. On the east side of the lake, 
weakly consolidated sands and gravels are exposed from 
the artificial 1,800-foot level of the lake to as high as 
2,300 feet above sea level; on the west side of the lake 
the gravels cap a ridge, and the base of the terrace gravels 
is about 200 feet above the lake. Old alluvium covers 
much of an old-land surface west of Laytonville Valley. 
Bedrock crops out within the area of the old surface as 
low, subdued hills, and according to Olmsted (1956, p. 
79) the alluvial cover between the hills probably is less 
than 50 feet thick in most places. A mile or two north 
of this old surface, a terrace at nearly the same altitude 
covers about two square miles along the southwest side 
of Tenmile Creek. It is underlain by unconsolidated sedi- 
ments, and has been entrenched to a depth of 200 feet by 
the creek and its tributaries. Recent alluvium covers most 
of Laytonville Vallev and is as much as 150 feet thick 
(Olmsted, 1956, p. 79). 

In the Klamath .Mountains province, areas of valley 
fill of Quaternary age generally are relatively small. The 
exceptions are Scott Valley, where alluvial fan deposits 
attain a probable thickness of 400 feet (Olmsted, 1956, 
p. 28-29), and Shasta Valley, adjacent on the east of the 
province, where broad areas are covered by glacial and 



alluvial deposits. The only other valleys of significant size 
in the Klamath Mountains are Weaverville, Hayfork, 
Hyampom, and Hoopa Valleys. Weaverville, Hayfork, 
and Hyampom Valleys are chiefly areas of rocks that are 
Tertiary in age, and alluvium of Quaternary age occurs 
only locally and as a thin veneer. Hoopa Valley is rela- 
tively narrow and consists chiefly of unconsolidated 
sands and gravels that underlie terraces at a succession 
of several levels; the principal high terrace is at an alti- 
tude of about 500 feet, approximately 200 feet above 
the Trinity River. According to Olmsted (1956, p. 56) 
individual terrace deposits along Hoopa Valley range in 
thickness from a thin edge to more than 35 feet. 

The bulk of the deposits of Quaternary age in the 
Klamath Mountains, with the exception of Scott Valley, 
occur as terraces in the valleys and on the canyon walls 
along the courses of the Smith, Klamath and Trinity 
Rivers and their tributaries, and as deposits in the stream 
beds. Some of the terrace deposits are as high as 400 feet 
above the present streams, and more than 100 feet thick. 
During the early days the terrace and stream gravels 
were mined extensively for placer gold. Owing to their 
economic interest they were studied along the upper 
reaches of the Trinity River by Diller (1911 and 1914a), 
who referred to them as auriferous gravels of the third 
cycle of erosion (Diller, 1911, p. 26-28). One deposit 
described by Diller (1911, p. 26-27) is a few miles south 
of Weaverville. It underlies a terrace 175 feet above the 
Trinity River. The upper 1 1 5 feet of the deposit is red- 
dish, poorly stratified clay, sand, and gravel. It is under- 
lain by 19 feet of blue gravels, sand, and clay, with a thin 
carbonaceous layer near the base. Fossil bones and shells 
are associated with the carbonaceous layer, and indicate 
a Pleistocene age. The bones are of mammoths, deer, and 
ground sloths, while the shells are similar to those of 
living fresh-water species (Diller, 1911, p. 27). Terrace 
deposits along the South Fork of the Salmon River have 
been described in detail by Hershey (1903d) in an at- 
tempt to relate the deposits to several glacial stages. 
Those along the Smith River have been described by 
Cater and Wells, (1954, p. 105-106, 124). 

Glacial Deposits. Alpine glaciers formed at many 
places in the Klamath Mountains and in an adjacent small 
area of the northern Coast Ranges, but none is now 
present. Evidence of the former presence of glaciers is 
at most places topographic, but deposits of glacial debris 
are found at some places. In many of the higher moun- 
tains, cirques, bedrock basins, marshy meadows, and 
U-shaped vallevs are common features of the landscape 
(photo 14) (see Davis, 1933, p. 215, figs. 19, 20; Hinds, 
1952, p. 139-142, fig. 100). Small lakes associated with 
these features are abundant, generally at altitudes above 
6,000 feet in the eastern part of the province, and at 
altitudes above 5,000 feet along the boundary between 
Siskiyou and Del Norte Counties in the western part. 
Diller (1902, p. 58) notes that on the northeast slopes 
of both North Yolla Bolly Mountain at the south end 
of the Klamath Mountains, and South Yolla Bollv Moun- 



1960] 



Northern Coast Ranges and Klamath Mountains 



55 




Photo 14. Aerial view of the Trinity Alps, looking northwest toward the glaciated, upper reaches of Canyon Creek in the 
northeastern part of the Helena quadrangle. Arrow points to Thompson Peak (altitude 9,002 feet), rlie highest point in the Klamath 

Mountains province. Photo GS-OAD, S-SO, September 19S3. 



tain nearby in the northern Coast Ranges, ". . . there 
were formerly glaciers a number of miles in extent which 
have left well-defined records in striated and polished 
nicks and ground moraines, with small lakes and mead- 
ows above terminal embankments." Southward along the 
high divide to near Anthony Peak, marshy meadows and 
vague cirque-like features suggestive of former glaciation 
were seen during the present reconnaissance. According 
to Holway (1914), evidence of former glaciation, such 
as striae on bedrock, small cirques, and moraines, is seen 
as far south as Snow Mountain along the high divide east 
of Lake Pillsburj . 

Detailed descriptions of some of the glacial features of 
the eastern part of Klamath Mountains have been given 
by Hcrshey (190(1, 1903a, 1903c, 1903d), The glaciers 
ranged from 2 to 15 miles in length, from one-fourth to 
a mile in width, and from 500 to 1,500 feet in thickness 
(Hershev, 1900, p. 45-49). He considered the latest stage 
of glaciation to be Wisconsin in age, an intermediate 
stage to be low an, and the earliest to be at least as old as 
lllinoian and perhaps as old as Kansan, the three stages 
corresponding to high, intermediate and low terrace de- 
posits along the South Fork of Salmon River (Hershev, 
1903d, p. 453-454). At one locality, Hershev (1903a, p. 
140) found fossil tusks of a mammoth embedded in an 
old soil formed at the surface of a glacial till. 



Volcanic Rocks. Volcanic flows, tuff beds, and cones 
arc conspicuous features in the vicinity of Clear Lake 
in the northern Coast Ranges, and have been described 
by Becker (1888), Anderson (1936), and Brice (1953). 
None have been found in the Klamath Mountains, al- 
though they are abundant in the Cascade Ranges adja- 
cent to the east. During the present reconnaissance the 
volcanic rocks of the Clear Lake area were not studied, 
and the following brief description is based on detailed 
work by Anderson (1936). 

.Mount Konocti, the principal volcanic landmark of 
the area, is an eroded multiple volcano on the west side 
of Clear Lake, and rises to an altitude of 2,800 feet above 
the level of the lake. It consists chiefly of a series of rhyo- 
dacitic flows that is underlain by rhyolitic pyfoclastic 
rocks. South and southeast of Mount Konocti, dacite and 
rhyolitic obsidian that are somewhat older cover an area 
of about 12 square miles. They probably are middle or 
late Pleistocene in age if the Cache formation is as young 
as early Pleistocene, judging from the absence of frag- 
ments of these rocks in the Cache formation, and from 
their stagjc of erosion. East of Clear Lake, rhyodacite that 
may be related to that of Mount Konocti, although per- 
haps nor extruded from the same vent, rests on deformed 
Cache formation. 

Recent lava flows and cinder cones, perhaps no older 
than a few thousand years, occur principally on the east 



56 



California Division of Mines 



Bull. 179 




Photo 15. Debris flow in area of Franciscan formation. View looking southwest from near Mendocino Pass, 

about 3 miles south of Anthony Peak. 



side of Clear Lake. They are largely andesites and basalts. 
At some places, notably Sulphur Bank, they have been 
altered greatly by solfataric action, and have been ex- 
ploited for their sulfur and quicksilver content. 

Landslide Deposits. Landslides are striking and abun- 
dant features in much of northwestern California, partic- 
ularly in the Coast Ranges. They are most common and 
widespread throughout the central belt of Franciscan 
formation where they are perhaps the foremost mode 
of degradation of the landscape. Although many of the 
landslides are measurable in terms of square miles, few 
are shown on the geologic map (pi. 1). 

Most of the landslides of the central belt of Franciscan 
formation appear to be debris flows (photo 15) rather 
than rotational slump blocks, and the debris generally 
consists of sheared and jumbled masses of graywacke, 
shale, greenstone, chert, glaucophane schist and serpen- 
tine. Many of these debris flows are characterized by 
grassy slopes that are nearly devoid of trees and brush. 
At places they occur along broad northwest-trending 
belts, and some of these belts can be traced many miles 
by means of the grassy slopes through terrain which 
otherwise is covered by brush and trees. These belts seem 
likely to be the traces of broad shear zones, owing to 
their linearity, the generally sheared character of the 
debris, and the presence of glaucophane schist and ser- 
pentine. 

Intrusive Rocks 
Granitic Rocks 

The term granitic rocks is used in this report as a con- 
venience in referring to plutonic crystalline rocks that 



range chiefly from diorite to granodiorite in composi- 
tion; true granite occurs at relatively few places. The 
granitic rocks are exposed over many hundreds of square 
miles in the Klamath Mountains province. In the north- 
ern Coast Ranges, granitic rocks are known only in two 
small areas a few acres in extent, but in the central and 
southern Coast Ranges granitic rocks crop out over large 
areas. Both areas of granitic rocks in the northern Coast 
Ranges are too small to be shown on the geologic map 
(pl. 1). 

In the Klamath Mountains of California the granitic 
rocks are widely distributed, and are found within all of 
the principal areas of stratified rocks of pre-Cretaceous 
age. In the southern half of the province the granitic 
rocks occur in two rudely defined belts that reflect the 
Klamath Mountains arc. The eastern belt of granitic rocks 
includes the Shasta Bally batholith at the southern end as 
well as other batholiths and smaller plutons northward 
along the central metamorphic belt, the eastern Paleozoic 
belt, and areas of ultramafic intrusives. The western belt 
of granitic rocks is chiefly in the western Paleozoic and 
Triassic belt. The largest body of granitic rocks of the 
western belt extends northwesterly from Hayfork Valley 
about 50 miles, and is herein referred to as the Ironside 
Mountain batholith for its exposure on a mountain of 
that name in the southwestern part of the Ironside Moun- 
tain quadrangle (fig. 2). The Ironside Mountain batho- 
lith is remarkably elongate and is the largest single area 
of granitic rocks exposed in the Klamath Mountains 
province. Other bodies of granitic rock included in the 



I960] 



Nor i in kn C< 



Ranges vnd Klamath Mountains 



^ _ 



w estern belt are several plutons southeast of Hayfork 
Valley, as well as several relatively small elongate plutons 
to the west along the east side of the belt of South Fork 
Mountain schist. 

The granitic rocks of the western belt are chiefly 
hornblende diorite, whereas those of the eastern belt arc 
chiefly quartz diorite and granodiorite. The rocks of the 
western belt have not been described in the literature. 
but those of the eastern belt have been described in some 
detail bv Hinds ( 1934, p. 182-192, and 1935, p. 336-354), 
Kinkel, Hall, and Albers I 1956), and Gay (1949). 

In the northern half of the Klamath Mountains of Cali- 
fornia the granitic rocks are not amenable to subdivi- 
sion into two belts. Maxson (1933, p. 128-129, 131-134, 
and pi. 4) described the principal areas of granitic rocks 
in eastern Del Xortc and western Siskiyou Counties as 
the Siskiyou granodiorite and the subordinate Preston 
hornblende diorite. The name Wooley Creek batholith 
is herein applied to the area of granitic rock that is 
drained largely by Wooley Creek and that covers much 
of the Marble Mountains wilderness area in southwestern 
Siskiyou County. This batholith consists largelj of quartz 
diorite that is rich in hornblende and biotite. Many large 
boulders of an unusual garnet-bearing facies of the quartz 
diorite were seen along Elk Creek in E'/2 sec. 32, T. 15 
N., R. 8 I-".. The boulders consist of medium-grained, 
hornblende-biotite-rich diorirc with euhedral crystals of 
reddish-brown garnet approximately one inch in diam- 
eter distributed throughout. On the geologic map (pi. 1) 
the Wooley Creek batholith is shown as a solid mass of 
granitic rocks, and it appears to be nearly as large as the 
Ironside Mountain batholith. However, much of the cen- 
tral area of the batholith was not traversed timing the 
reconnaissance, and the outline of the batholith, particu- 
larly near the upper reaches of Wooley Creek, is poorly 
known. In the northeastern part of the Seiad 30-minute 
quadrangle the granitic rocks arc quartz diorite and gran- 
odiorite (Ryncarson and Smith, 1940, p. 285-286, 287). 
Further east, in the northern part of the Yrcka 30-minute 
quadrangle, the prevailing granitic rocks were mapped as 
diorite and granodiorite (Avcrill, 1931, plate in pocket). 

Granodiorite intrudes diorite at several widespread lo- 
calities in the Klamath Mountains province. This relation, 
in addition to other admittedly inconclusive data, has 
been considered by Hinds (1932, p. 406-407, and 1934, 
p. 186) and Maxson (1933, p. 128-129) to indicate two 
distinct and w idely spaced periods of intrusion of gra- 
nitic rocks, the diorirc being emplaced during the Late 
Paleozoic, and the quartz diorite and granodiorite during 
the Late Jurassic. They describe exposures where the 
granodiorite or related rocks intrude diorite, and accord- 
ing to Hinds the diorite does not intrude rocks younger 
than the Bragdon formation of Mississippian age. How- 
ever, in other parts of the Klamath Mountains province, 
in Oregon as well as in California, thorite intrudes rocks 
as young as the Applcgate group of Triassic(r) age 
(Wells, 1955) and the Galice formation of Late Jurassic- 
age (Cater and Wells, 1954, p. 99; Wells, Hotz, and 



Cater, 1949). "Hie diorite presumably was emplaced dur- 
ing the same general period as the more fclsic intrusive 
rocks, during Late Jurassic or Cretaceous time. 

The age of the quartz diorite and the related more 
fclsic rocks has been argued by many geologists, w ith 
respect both to field relations observed in the Klamath 
Mountains province and by comparison to the Sierra 
Nevada batholith with which the granitic rocks of the 
Klamath region have commonly been related through 
broad speculation. The principal arguments have been 
summarized by Hinds (1934, p. 182-184). 

The lower age limit of the so-called younger granitic 
rocks of the Klamath Mountains province has been based 
previously (Hinds, 19H, p. 189) on intrusion of the 
Potem formation of Middle Jurassic age (Diller, 1906). 
How ever, it appears that the lower limit can be placed 
in the Late Jurassic on the basis of relations observed 
elsewhere in the province. In the Gasquet quadrangle, 
according to Cater and Wells (1954, p. 92-104), the 
Galice formation of middle Late Jurassic (late Oxfordian 
to middle Kimmeridgian) age is intruded by ultramafic 
rocks that in turn arc intruded by diorite, as well as 
by dikes of quartz thorite that are ". . . thought to be 
highly silicic differentiate of the main hornblende diorite 
body . . .". In the Kerby quadrangle, Oregon, the Calice 
and Dothan formations are intruded by a large body 
of hornblende diorite and related but more felsic rocks 
(Wells, Hotz, and Cater, 1949). 

Granitic rocks are overlain by gently-dipping strata of 
Cretaceous age at two general localities along the eastern 
border of the Klamath Mountains province. In Califor- 
nia and Oregon, near their common boundary north of 
Shasta Valley, the Hornbrook formation (Peck, Imlay, 
and Popenoe, 1956) of Late Cretaceous age lies on the 
stripped and eroded surface of a quartz diorite batholith. 
Strata of Early Cretaceous age lie similarly on the Shasta 
Ball) batholith southwest of Redding, and with high 
angular unconformity on the strata of pre-Latc Jurassic 
(middle Tithonian) age that are intruded by the granitic 
rocks. The strata that overlie the Shasta Bally batholith 
are reported to range from Valanginian to Hauterivian 
in age (Hinds, 1934, p. 189-190), and pebbles of quartz 
diorite thought to be derived from the Shasta Bally 
batholith or similar intrusive bodies are found in nearby 
strata as old as basal Paskenta (Hinds, 1934, p. 190). 
However, doubt has been cast that the Shasta Bally 
batholith is overlain by strata older than lowermost 
Horsetown (see Murphy, 1956. p. 2102-2105. fig. 4). 

The Knoxvillc formation is critical in dating precisely 
the emplacement of the Shasta Bally batholith. Hinds 
(1934, p. 191) notes the likelihood of the period of 
granitic intrusion being pre-Knoxville formation in aye 
if Knoxvillc strata overlie the strata of the Klamath 
Mountains province. This relation is reported by Ander- 
son (1945, p. 926-927). Viewed more broadly, however, 
the emplacement of the Shasta Bally batholith must in- 
deed pre-date the Knoxville formation, as strata of the 
Shasta series overlie the .Shasta Bally batholith vv ith ero- 



58 



California Division of Mines 



[Bull. 179 



sional unconformity, and as the Shasta series is generally 
conformable with the Knoxville in a long belt that ex- 
tends from near latitude 40 degrees southward to near 
Wilbur Springs. The writer would expect to find a 
marked angular unconformity between the Knoxville 
formation and the Shasta series, if the Shasta Bally batho- 
lith had been emplaced after the deposition of the Knox- 
ville formation. If the granitic rocks of the Klamath 
Mountains province be considered to have been emplaced 
during a single period, the period would seem most likely 
to be post-Galice formation (late Oxfordian to middle 
Kimmeridgian) and pre-Knoxville formation (middle 
Tithonian). 

The two known localities of granitic rocks in the 
northern Coast Ranges are not shown on the geologic 
map (pi. 1), as neither of them appear to be more than 
a few acres in extent. One of the localities is in the 
northern part of the Eureka quadrangle, in SE'/jNW 1 / 
sec. 8, T. 6 N., R. 1 E., about a quarter of a mile north 
of the Mad River and a few hundred feet east of High- 
way 101, where large blocks of medium-grained syenite 
occur on a brush-covered hillside. The blocks are as 
much as 15 feet long, and once were quarried on a small 
scale for tombstones. Higher on the hillside, weakly con- 
solidated mudstone, sandstone, and conglomerate are ex- 
posed in a small area, and the conglomerate contains 
abundant pebbles and cobbles of granitic rock. It is not 
clear whether the large blocks of syenite came from an 
intrusive body nearby, or whether they are unusually 
large blocks from the weakly consolidated conglomerate. 

Ultramafic Rocks 

Ultramafic rocks are abundant in the northern Coast 
Ranges and Klamath Mountains provinces. Peridotite is 
the prevailing type of ultramafic rock, but dunite is im- 
portant locally. Pyroxenite and hornblendite are rela- 
tively uncommon. Small bodies of gabbroic and diabasic 
rocks are widely associated with the ultramafic rocks, 
and are generally thought to be related genetically. Most 
of the ultramafic rock has been altered to serpentine to 
a considerable extent, and indeed is commonly referred 
to as "serpentine" by field geologist and human alike. 

The peridotite ranges in color from green to nearly 
black where fresh, and brown where weathered. It com- 
monly is coarse grained, and the coarse-grained texture 
remains evident even in many areas where the rock has 
been altered almost completely to serpentine. Soil de- 
rived from the peridotite and other ultramafic rocks 
commonly is red-brown in color, and generally supports 
only brush and a sparse growth of timber. 

The ultramafic rocks generally occur as rudely tabu- 
lar bodies. Some have been considered to be sills, whereas 
others occur along fault zones. Generally they are highly 
sheared. Some are thought to have intruded in a molten 
state, but others, according to some geologists, may have 
been emplaced by so-called cold or plastic intrusion (see 
Taliaferro, 1943, p. 202-206). Commonly the contact 
between the ultramafic and adjacent rock is not exposed 



sufficiently to permit direct observation as to whether it 
is one of intrusion or faulting. 

Because of probable structural dislocation of many of 
the bodies of ultramafic rock, the age or ages of intrusion 
are not readily apparent. The ultramafic rocks of the 
Klamath Mountains may be of a different age from those 
of the Coast Ranges, and even those within a single prov- 
ince may not be all of one general age. In the Klamath 
Mountains, ultramafic rock occurs as sill-like bodies in 
the Applegate group, and intrudes the Galice formation 
(Wells and Cater, 1950, p. 81). Maxson (1933, p. 131 
and fig. 7) notes that the ultramafic rock intrudes the 
Galice formation, and is in turn intruded by, and occurs 
as xenoliths in, Siskiyou granodiorite. Southwest of Red- 
ding, strata of the Horsetown formation of late Early 
Cretaceous age overlie a belt of ultramafic rocks ad- 
jacent to the west side of the Shasta Bally batholith. 
Owing to the broadly conformable relation of the Knox- 
ville and Horsetown formations, the ultramafic rock 
overlain by the Horsetown would seem most likely to 
be pre-Knoxville in age. Thus, if the ultramafic rocks 
southwest of Redding are the same age as those that in- 
trude the Galice, thev must have been emplaced between 
the middle Kimmeridgian and middle Tithonian stages 
of the Late Jurassic. The available data suggest that the 
ultramafic and granitic rocks of the Klamath Mountains 
were emplaced during the same general interval of time, 
the ultramafic rocks preceding the granitic rocks. 

In the northern Coast Ranges, ultramafic rocks are 
widespread throughout the Franciscan rocks of the cen- 
tral belt. At most places their relation to adjacent rocks 
has not been proved, but at some places they doubtless 
are intrusive. As the Franciscan rocks, however, may be 
restricted to the Late Jurassic in age, or may range from 
Late Jurassic to early Late Cretaceous, the age of the 
ultramafic intrusion is not closely known. Near Wilbur 
Springs and Knoxville, thick stubby lenses of sedimentary 
serpentine occur in the Knoxville and Paskenta forma- 
tions (Averitt, 1945, p. 73-74, and fig. 2; Taliaferro, 1943, 
p. 206-207); these presumably represent submarine land- 
slides from nearby serpentine bodies that were exposed 
during the Late Jurassic and earliest Cretaceous. Ac- 
cording to Taliaferro (1943, p. 202-205) the Knoxville 
formation is intruded by ultramafic rocks. 

STRUCTURE 

The structure of northwestern California is complex, 
and is not amenable to detailed description and interpre- 
tation on the basis of brief reconnaissance such as the 
present study. Undoubtedly the area has been mobile 
throughout much of the time from the Paleozoic to the 
present. Owing to the resulting structural complexities 
and to the close lithologic similarities and generally poor 
exposures of many of the formational units, the broad 
structural relations are not accurately known even in 
those few quadrangles that have been studied in com- 
parative detail by other workers. The situation is similar 
in adjacent areas from which data might be extrapolated, 
such as the northern continuation of the Klamath Moun- 



I960! 



Northern Coast Ranges and Klamath Mountains 



59 



tains in southwestern Oregon and the southern continu- 
ation dt' the northern Coast Ranges to the San Francisco 
Bay area. The pattern of the lifliic units shown on the 
geologic map (pi. 1) may he a clue to the structure of 
the area, hut a clear knowledge of the structure of north- 
western California must await painstaking study in the 
field. 

In both provinces, the strata most commonly dip east- 
ward. Faults in the northern Coast Ranges are generally 
at a high angle and are part of the northwest-trending 
San Andreas system of dominantly strike-slip and high- 
angle faults. Some of these faults, however, doubtless 
have a significant vertical component, as shown by ver- 
tical offset of Tertiary ami Pleistocene strata, and may 
be chief!) dip-slip. The dominant structural elements of 
the Klamath .Mountains province appear to be a scries of 
concentric moderate to high-angle reverse faults over 
which the rocks of the province were thrust southwest- 
ward. 

The boundaries between the Klamath .Mountains and 
the Coast Ranges, and between the Coast Ranges and the 
Sacramento Valley, doubtless are major tectonic features 
of the Pacific Coast region, but they have been given 
only scant attention by geologists. A small segment of 
the San Andreas fault, another tectonic feature of great 
magnitude, is in the southwestern part of the map area, 
beyond which to the northwest it is covered by coastal 
water. It is better known than the province boundary 
structures, as it has been studied much in central and 
southern California. 

The province boundary between the Klamath .Moun- 
tains and the Coast Ranges was first drawn by Oilier 
(1894b, pi. 40), and later was modified (Diller, 1921, 
lig. 1). Diller (1902, p. 9-10) defined the boundary on 
the basis that the Klamath Mountains ". . . are composed 
largely of sedimentary and igneous rocks, similar to those 
of the Sierra Nevada. . . ." and that the drainage of the 
Klamath .Mountains, in contrast to the Coast Ranges, is 
transverse rather than in general parallel to the strike of 
the rocks. However, the two features that form a basis 
for drawing a boundary do not coincide exactly, and 
Diller appears rather clearly to have drawn much of the 
boundary in favor of lithology and geomorphic history 
rather than drainage. Along the South Pork Mountains, 
for example, Diller drew the boundary on the southwest 
side to include the South Fork Mountain schist in the 
Klamath Mountains province, despite the fact that the 
South Pork of the Trinity River on the northeast side 
of the ridge is parallel not only to the strike of the rocks 
bur to the principal rivers of the Coast Ranges. On the 
other hand, in the western parr of the Klamath .Moun- 
tains of Oregon Diller included large areas of rocks 
equivalent to those of the Sacramento Valley sequence, 
that is, rocks that are not common to the Sierra Nevada. 

Northwesterly from the South fork Mountains, the 
boundary line of Diller (1921, fig. 1) is along Redwood 
Creek, and thereby includes in the Coast Ranges the Red- 
wood Mountain belt of schist although it is similar to the 



Si Miih I'oik Mountain schist of the Klamath Mountains. 
Along the same interval it includes in the Klamath Moun- 
tains a belt of rocks that appear to be related to the 
Franciscan formation rather than to the Galice or older 
formations of the Klamath .Mountains. Some geologists 
(for example see Taliaferro and Hudson, 1943, p. 219) 
consider the boundary to intersect the coastline about 6 
miles southwest of Orick, thus including the Redwood 
Mountain belt of schist within the Klamath Mountains 
province, but excluding the smaller area of schist to the 
west. 

The southern extremity of the Klamath Mountains 
province of Diller is a lobe that extends southward 
slightly beyond the latitude of Paskenta. The boundary 
here may have been drawn to include within the Klamath 
Mountains province several high peaks such as Ovenlid, 
South Yolla Polly, Harvey, Sugarloaf, Hammerhorn, and 
Anthony, some above 7,000 feet in altitude, rather than 
on the basis of lithology. Or perhaps Diller did not con- 
sider that the rocks, south of the southeast-trending belt 
of schists that underlie North Yolla Bolly Mountain, are 
Franciscan rather than formations that are generally con- 
sidered to constitute the Klamath Mountains. 

The boundary line between the Klamath Mountains 
and the Coast Ranges as drawn by the writer (see fig. 1) 
more consistently outlines the two major groups of for- 
mational units of northwestern California. In addition it 
more clearly reflects the structural and lithic grain of the 
Klamath Mountains arc. The boundary excludes from 
the Klamath Mountains the two areas of schist that are 
isolated in an area w hich otherwise is characteristic of 
the Coast Ranges. The boundary is along the southwest- 
ern slope of a prominent high ridge that is nearly con- 
tinuous from the Oregon border to the Sacramento Val- 
ley, a distance of approximately 150 miles. The ridge has 
been notched deeply by the Klamath and Smith Rivers 
on their courses to the sea. Names applied to various 
intervals from northwest to southeast along the ridge 
include, among others, Rattlesnake Mountain, Red 
Mountain, Blue Creek Mountain Ridge, Pine Ridge, In- 
dian Field Ridge, South Fork Mountains, North Yolla 
Bolly Mountain, ami Tomhead .Mountain. North of the 
notch cut by the Klamath River, much of the ridge is a 
belt of ultramalic rock, but south of the Klamath River 
the ridge is chiefly schist. As the boundary is drawn, the 
formational units of the Klamath Mountains province are 
of late Jurassic (Kimmcridgian) and older ages, with 
the exception of a few small patches of younger rocks, 
and, with the same exception, have been intruded by sig- 
nificant quantities of granitic rocks. The formational 
units of the northern (oast Ranges of California, with 
the exception of two isolated areas of schist that may be 
related to the schist of South Fork Mountain, are all 
thought to be younger than Kimmcridgian in age, and 
generally arc not intruded by granitic rocks. 

The boundary between the Klamath Mountains prov- 
ince and the Coast Ranges has long been considered to be 
a fault along which the schists of South Fork .Mountain 



60 



California Division of Mines 



[Bull. 179 



have been thrust southwestward over the rocks of the 
Coast Ranges. The origin of this concept has been attrib- 
uted to O. H. Hershey and others by Diller (1915, p. 
52), and although the concept has gained wide recogni- 
tion (Fenneman, 1931, p. 469-470; King and others, 
1944) the writer can find little record of its having been 
substantiated by conclusive data. Taliaferro and Hudson 
(1943, p. 219), however, state that the boundary is a 
thrust fault that dips northeast 40° to 45° near the south- 
east end of the South Fork Mountains. During the pres- 
ent reconnaissance, nearly the entire length of the 
boundary along the southwest slope of the South Fork 
Mountains and related ridges was seen to be mantled by 
landslide debris, and the contact between the rocks of 
the two provinces generally is concealed. Marked large- 
scale irregularities in the contact were not seen at the 
various notches along the ridge where one might expect 
them to be if the contact is a low-angle reverse fault. 
The fault seems most likely to be steep, judging from the 
apparent uniformity of the trend of the boundary for a 
distance of more than 100 miles from south-central Trin- 
ity County to near the Oregon border. 

The two belts of schist west of the boundary of the 
Klamath Mountains, isolated from the Klamath Moun- 
tains by presumably younger rocks of the Coast Ranges, 
are most readily explained by means of a series of alter- 
nate normal and reverse faults that trend nearly parallel 
to the boundary fault. The western boundary of each 
belt of schist appears to be a reverse fault, the schist 
being thrust westward over adjacent rocks of the Fran- 
ciscan formation. Taliaferro and Hudson (1943, p. 219) 
consider the western contact of the principal isolated belt 
of schist to be a northward continuation of the boundary 
thrust of the South Fork Mountains, and to dip steeply 
to the northeast. According to S. J. Rice (oral communi- 
cation, 1955) the contact between the principal belt of 
schist and the Franciscan formation to the west is well 
exposed in the east-central part of the Trinidad quad- 
rangle (fig. 2), and is a fault that dips about 60° NE. He 
considers the small area of schist near Trinidad to be 
thrust westward over the Franciscan formation, but to 
be in contact with the upthrown Franciscan formation to 
the east along a normal fault. Although the pattern of 
distribution of the belts of schist bounded on the west by 
reverse faults is most easily explained if the eastern 
boundaries of the schist belts are considered to be normal 
faults. Manning and Ogle (1950, p. 27) state that in the 
Blue Lake quadrangle the Franciscan rocks have been 
thrust westward over schist along the east side of the 
Redwood Mountain belt. 

The southern boundary of the Klamath Mountains 
province is along the base of the southern slope of a bold 
ridge of schist that includes North Yolla Bolly Mountain 
and Tomhead Mountain. The ridge trends about N. 65° 
W., diverging sharply from the N. 30° W. trend of the 
South Fork Mountains. The boundary was crossed at 
only two places during the present reconnaissance, as the 
area is remote and access is difficult. Judging largely from 



inspection of aerial photographs, the boundary seems 
most likely to be a vertical or high-angle fault. 

Transverse faults in adjacent provinces are aligned 
with the southern boundary of the Klamath Mountains. 
One is nearby to the east in the Sacramento Valley 
province, where strata of Late Jurassic and Cretaceous 
ages are offset with an apparent left-lateral displacement 
of several miles. To the northwest, in the Eel River 
Valley area of western Humboldt County, the faults 
chiefly trend nearly west, and according to Ogle (1953, 
pi. 2) they are high-angle reverse faults. The area south 
of the Eel River Valley area, to the Mattole River, is 
one of considerable structural complexity. The northern 
part of this area has been described by Ogle (1953, p. 
22-24) as the False Cape shear zone. On the geologic map 
(pi. 1 ) the area is shown as chiefly uppermost Cretaceous 
rocks, but, as noted by Ogle (1953, p. 22-24), it includes 
complexly in-folded and in-faulted blocks of Franciscan 
and Tertiary rocks. The axes of at least some of the in- 
folds trend westward (Hoots, 1928) parallel to the 
structural axes of the Eel River Valley area. Thrust 
faults likely are present, as a hole drilled for oil is re- 
ported to have intersected rocks of Tertiary age after 
penetrating older rocks to a depth of 4,000 feet. 

The Gorda submarine escarpment (pi. 1) is another 
transverse structure, and although it is somewhat south 
of the line of the southern boundary of the Klamath 
Mountains province, it appears likely to be related. The 
Gorda escarpment is a north-facing scarp that extends 
west from Cape Mendocino. Here the base of the steep 
continental slope ranges approximately between 1,000 
and 1,600 fathoms, and along the escarpment it is offset 
in a manner that might be ascribed to right-lateral 
faulting with an apparent displacement of several tens 
of miles. The structure continues due west for at least 
1,400 miles, and has been referred to as the Mendocino 
escarpment (Menard, 1955). West of the westernmost 
projection of the continental slope, however, the escarp- 
ment faces south rather than north. It ranges from 3,300 
to 10,500 feet high, and north of the escarpment ". . . 
the sea floor for hundreds of thousands of square miles is 
about half a mile higher than the floor to the south." 
(Menard, 1955, p. 36-37.) 

The strata of the northern Coast Ranges have been 
folded and faulted, and as the resulting structure is of a 
complexity that does not lend itself to solution by re- 
connaissance, the writer can add little to the knowledge 
of the structure of the area. The province includes a 
great abundance of faults that in general trend northwest. 
Near the latitude of Cape Mendocino the northwest 
trend is intersected by more westerly, transverse struc- 
tures that have already been described. Folds in the strata 
appear fairly broad, and at the few places where the 
trends of the axes of the folds are known, the trends 
generally are nearly parallel to the trend of the faults. 
Some of the fold axes in the Gualala series west of the 
San Andreas fault trend westward at a large angle to 
the fault. The strata most commonly dip gently to 



19601 



Northern Coasi Ranges \m> Klamath Mountains 



61 



steeplv northeast, but it is oversimplification to state 
that the structure of the northern Coast Ranges is 
merely one of fault blocks that are tilted northeast. 

Only the most important faults are shown on the geo 
logic map (pi. 1). Faults are abundant, however, par- 
ticularly in the central belt areas of interbedded detrital 
sedimentary rocks, chert, and volcanic rocks. Not only 
are these rocks sheared and dislocated, hut small bodies oi 
glaucophane schist and highly sheared lenses ol serpen- 
tine occur in them along fault lines. Additional evidence 
of faulting that is particularly common within the Fran- 
ciscan formation of the central belt is the abundance of 
so-called faultline ridges, saddles, valleys, sag ponds, and 
landslides. All of the major intermountain valleys ol the 
northern Coast Ranges are cither entirely or partly 
within areas of the Franciscan formation, and they have 
been formed at least partly by faulting. 

A fault extending N. 3~ W. from Fort Ross to a point 
5 miles northeast of Point Arena is the northernmost ex- 
posed segment of the San Andreas fault. Northward the 
fault continues to sea. Southward the fault also is covered 
by coastal water, but the same fault, presumably, has 
been projected across narrow exposures of land near 
Bodega Head and Tomalcs Bay and thence projected to 
the west coast of the San Francisco Peninsula. Southward 
from the San Francisco Peninsula the San Andreas 
fault has been traced approximately 600 miles, and con- 
sidered to be a right-lateral fault with perhaps great 
strike-slip displacement. Along the central and southern 
Coast Ranges of California it is a boundary between the 
Franciscan formation to the east, and granitic and meta- 
morphic rocks to the west. Tertiary rocks also are 
abundant west of the fault. The presence of granitic 
rocks west of the fault at Bodega Head and Tomalcs 
Bay, as well as at Cordell Bank about 20 miles offshore 
from Point Rexes (Hanna, 1952, p. 364; Chesterman, 
1952, p. 360-361 ). suggests that the fault projected to 
near Point Arena is indeed the northern continuation of 
the San Andreas fault, even though granitic rocks are 
not found west of the fault between Fort Ross and Point 
Arena. The fault between Fort Ross and Point Arena 
separates the Gualala series of late Fate Cretaceous and 
early Tertiary ages to the west, from strata to the east 
that arc of early Fare Cretaceous and perhaps older ages. 

Shortly after the well-known San Francisco earth- 
quake of 1906, scarps and other evidence of movement 
along the San Andreas fault could be traced southward 
from Point Arena to Fort Ross, across Bodega I lead and 
at the southeast end of Tomales Bay, and on the San 
Francisco Peninsula and southward (Lawson and others, 
1908, p. 53-151). Similar effects of movement along a 
fault were seen at Point Delgada and northwest toward 
Petrolia, and these xvere considered to indicate the con- 
tinuation of the San Andreas fault beyond Point Arena 
(Lawson and others, 1908, Atlas, map no. 1; King and 
others, 1944). The fault thus projected beyond Point 
Arena would deviate markedly from its otherwise re- 
markably uniform northwestward trend where it is ac- 



curately known south of Point Arena, and would follow 
the coastline in a northerly direction in order to resume 
a northwestward trend from Point Delgada toward 
Petrolia. Shepard and Emen I 1941, p. 38-39, and fig. 1m 
conclude that from Point Arena, the San \ndrcas fault 
closel) follows the coastline even beyond Point Delgada. 
curving westward to sea to continue as the Mendocino 
fracture /one along the Gorda escarpment. 

In projecting the San Andreas fault beyond Point 
\rena. the fact that the Coast Ranges arc a broad zone 
ot northwest-trending fault blocks should he considered, 
and although the San Andreas fault may he the master 
fault of the system, some other faults of the system also 
are of major magnitude. It also is significant that the 
Franciscan formation, including greenstone, chert, and 
gra) wacke, crops out west of the fault at Point Delgada; 
elsewhere in the Coast Ranges, to the southeastward be- 
yond the report area, the Franciscan rocks rarely occur 
in the Nacimiento-San Andreas fault block west of the 
San Andreas fault. As noted by Shepard and Emery 
I 1941, p. 38-39), the coastline in the vicinity of Point 
Delgada appears to he controlled by a fault. The coast- 
line for a distance of 20 miles in either direction from 
Point Delgada trends northwest, nearly parallel to the 
general trend of the faults of the system, and is aligned 
with an apparently major fault that trends northwest 
along the east side of the coastal belt of sedimentary 
rocks near YVillits. It seems likely that although the fault 
at Point Delgada is probably parallel to the San Andreas 
fault, it is several miles to the northeast, and that beyond 
Point Arena the San \ndrcas fault continues seaward 
along its regular northwest trend. 

Differences of opinion exist as to xvhether the San 
Andreas fault continues northwestward beyond the Men- 
docino fracture zone. As previously mentioned, Shepard 
and Emery ( 1941, p. 38-39) consider the San Andreas 
fault to continue west along the .Mendocino escarpment, 
and ask, "What could be more likely than that one of 
the greatest of all land faults should extend out to sea 
as one of the most remarkable of all submarine escarp- 
ments?" However, if the submarine configuration of the 
San Andreas fault in the vicinity of the Mendocino frac- 
ture /one is analogous to its configuration along the 
Transverse Ranges of southern California where it is 
intersected by the Murray fracture /one (Menard, 1955, 
fig. 2), it might he expected to curve westward and then 
resume its regular northwestward trend northward 
beyond the fracture zone. Menard (1955, p. 1193) con- 
siders the San Andreas fault to cross the .Mendocino frac- 
ture zone, ami. based on the location of epicenters, to 
continue to a point some distance west of the coast of 
Oregon. Whether these epicenters arc along the San 
Andreas fault, or are along another fault of the same 
system, probably will remain an academic question. 
Nevertheless it seems likely, as stated by Menard (1955, 
p. 1193), that "Perhaps the San Andreas and related 
faults mark a great fracture zone produced b\" the same 



62 



California Division of Mines 



[Bull. 179 



stress as the submarine fracture zones and complementary 
to them." 

The boundary between the northern Coast Ranges and 
the Sacramento Valley, from near Wilbur Springs to the 
southern tip of the Klamath Mountains province, is an 
apparently continuous belt of serpentinized ultramafic 
rock. The ultramafic rock is sheared, and at some places 
encloses small lenses of strata that appear to be fault 
slices. The shear planes of the ultramafic rock are most 
commonly north-trending and steep, as is the foliation 
of the slaty rocks adjacent to the west. The eastward 
dip of the strata of the Sacramento Valley sequence 
steepens toward the belt of ultramafic rock, and in some 
places near the belt of ultramafic rock the strata are 
overturned. Although the structure is not clearly under- 
stood, the ultramafic rock appears to be in a zone of 
high-angle faulting along which the slaty rocks of the 
Coast Ranges to the west are in juxtaposition with the 
Sacramento Valley sequence of generally only mildly 
deformed rocks to the east. Taliaferro (1943, p. 209) 
states that the contact between the ultramafic rock and 
the Sacramento Valley sequence is a high-angle thrust 
fault that dips 60° to 65° W. in northern Glenn County, 
and a vertical fault in central Colusa County, but that at 
Redbank Creek, the contact is clearly intrusive. In 
essence, Taliaferro (1943, p. 210) considers the ultra- 
mafic rock to be a sill that ". . . intrudes the upper part 
of the Franciscan and the lower part of the Knoxville, 
but in some places it is wholly within either Knoxville or 
Franciscan." 

In the North Elder Creek area of Tehama County, the 
ultramafic mass where mapped by Rynearson (1946) is 
thought to be a dike inclined steeply westward, perhaps 
intruded along a pre-existing fault that separated east- 
ward-dipping strata of the Franciscan formation from 
similarly dipping strata of the Knoxville formation (Ry- 
nearson, 1946, p. 199). 

Although the overall trend of the belt of ultramafic 
rocks is slightly west of north, it consists of a series of 
alternate northerly and northwesterly trends. The north- 
erly trends are roughly parallel to the long axis of the 
Sacramento Valley, whereas the northwesterly trends are 
parallel to, and probably related to, the Coast Ranges 
system of faults. At three "hooks" in the belt of ultra- 
mafic rocks, one near Paskenta, another near Stonyford, 
and a third near Wilbur Springs, the local structure of 
the Knoxville formation is more complicated by folding 
and faulting than is usual. Near Wilbur Springs, the 
ultramafic rocks and strata of the Sacramento Valley 
sequence have been folded into an anticline that plunges 
gently southeastward. The belt of ultramafic rocks ends 
on the southwest flank of the anticline, to again continue 
a few miles south of the map area, but the strata of the 
Sacramento Valley sequence on the southwest flank of the 
anticline have been warped into a parallel syncline. These 
northwest-trending folds in the strata of the Sacramento 
Valley sequence near Wilbur Springs are in line with a 
major shear zone, marked in part by a narrow belt of 



ultramafic rocks, that trends northwestward to Lake 
Pillsbury and perhaps beyond. 

The trends of structures and lithic belts of the Kla- 
math Mountains form an arc that is convex westward 
(see fig. 3). In general, the south- and southeast-trending 
segment of the Klamath Mountains arc is in California, 
and the northeast-trending segment is in southern Ore- 
gon. As noted by Hershey (1903b), and elaborated by 
Diller (1915, p. 51-52), the structural trends in the north- 
ern part of the Klamath Mountains are aligned with the 
Blue Mountains of Oregon to the northeast, and those of 
the southern part are aligned with the structural trend 
of the northern part of the Sierra Nevada to the south- 
east. The Klamath Mountains thereby give the impression 
of a tectonic bulge in which the rocks have been pushed 
westward, and this seems to be supported by the few 
facts and inferences that can be drawn regarding the 
broad structure of the province. As previously described, 
the western boundary of the province appears to be a 
high-angle reverse fault that dips eastward. West of the 
boundary, similar faults are thought to occur along the 
west sides of outlying belts of schist similar to the schist 
of the South Fork Mountains. 

Hershey (1903b) was the first to give an hypothesis 
relating to the broad structure of the Klamath Mountains 
province. He considered the province to consist of two 
parallel synclinoria, one on each side of the belt of schist 
that includes the Abrams and Salmon formations. His hy- 
pothesis, at least with regard to the more westerly of 
these so-called synclinoria, seems to have been based 
largely on his correlation of the schist of the South Fork 
Mountains with the Abrams formation. He considered 
the schist to be continuous from the South Fork Moun- 
tains to the central metamorphic belt of Abrams and 
Salmon schists, the schists being overlain in the trough 
of the synclinorium by presumably younger rocks of 
Paleozoic age. His hypothesis appears erroneous, how- 
ever, as the South Fork Mountain schist is more likely 
correlative with the Galice formation of late Jurassic 
(late Oxfordian to middle Kimmeridgian) age, rather 
than with the Abrams formation. The Galice formation 
is found only along the western edge of the province, 
and it is unlikely on both stratigraphic and structural 
grounds that its schistose facies, the South Fork Moun- 
tain schist, underlies the broad belt of Paleozoic and 
Triassic rocks to the east and is continuous with the 
Abrams schist as was hypothesized by Hershey. In ad- 
dition, the strata immediately west of the central meta- 
morphic belt most commonly dip eastward; one would 
expect the adjacent strata to the west of the central 
metamorphic belt to dip westward if they are on the 
east limb of a synclinorium, unless they are overturned 
on a large scale. 

The principal faults appear to be chiefly along the 
boundaries between the lithic belts as shown on the 
geologic map (pi. 1), although at only a few places were 
these boundaries seen to be faults by field observation. 
Thev are somewhat similar in position to features de- 



1960] 



Northern Coast Ranges and Klamath Mot ntains 



63 



scribed briefly as major faults by Hershey (1903b, 1906, 
p. 58-59; also sec Lawson and others, 1908, Atlas, map 
no. 1). 

Two of the major faults postulated on the basis of the 
present reconnaissance of the Klamath Mountains prov- 
ince are rudely parallel to the western boundary of the 
province. One is along the w est side of the central meta- 
morphic belt, and extends from the Jurassic ami Cre- 
taceous overlap southwest of Redding northwestward 
to the Salmon River. Along much of its length the foli- 
ation of the strata on either side dips moderately to 
steeply northeastward, and the boundary seems likely to 
be a reverse fault whose attitude is nearly parallel to 
the foliation. Beyond the Salmon River the lithic grain 
is northeastward toward Scott Valley and Vreka, but 
whether the fault continues to or beyond Scott Valley 
is not clear. 

Another major fault appears to form much of the 
boundary between rocks of the w estern Jurassic belt 
that are intruded by relatively small quantities of granitic- 
rocks, anil strata of the western Paleozoic and Triassic 
belt that are intruded by abundant granitic rocks. In 
Trinity County, the fault for much of its length north 
of the Trinity River is along the contact between the 
( ialice formation and the west side of the Ironside Moun- 
tain batholith. Bodies oi sheared serpentine occur at each 
place the fault was crossed during reconnaissance, al- 
thought generally they are too small to show on the 
geologic map (pi. 1 ). Foliation ami bedding in the Galice 
formation near the fault generally dip eastward. The 
general dip of the fault most likely is steeply eastward. 



Southward from the Trinit) River the fault probablv 
continues along the west side of the Ironside Mountain 
batholith to the west end of Hayfork Valley, and from 
there may continue southeast forming a boundary be- 
tween an area of abundant ultramatic rock to the west 
and areas of granitic rocks to the east. In Siskiyou 
County the northward continuation of the fault is 
marked by a belt of ultramahc and mafic rock that, for 
about half the distance to Happy Camp, is along the cast 
side of the Klamath River. The fault has not been traced 
north of 1 lappv Camp. 

Maxson (1933, p. 136-138, and pi. 4) described three 
faults in Del Norte County. One he referred to as the 
Orleans fault after Hershey (1906, p. 58; also see Law- 
son and others, 1908, Atlas, map no. 1). It trends north- 
east nearly parallel to and a few miles west of the eastern 
boundary of Del Norte County, and is the contact be- 
tween the ( Ialice formation to the west ami a complex 
of ultramalic and granitic rocks to the cast. According 
to Maxson (1933, p. 136-137) it is a steep reverse fault, 
presumably dipping southeast, with a throw of several 
thousand feet. In the Gasquet quadrangle, where the 
reconnaissance of Maxson | 19V?) is superseded b\ more 
derailed mapping by Carer ami Wells (1954, pi. 11 ), the 
so-called Orleans fault is not shown, but it might well 
trend along a belt of ultramafic rock. 

A second fault referred to by Maxson (1933, p. 137, 
and pi. 4) is along the west side of the serpentine ridge 
that marks the western limit of the Klamath .Mountains 
province south of the Smith River in the Crescent City 
quadrangle. It was considered to be a possible continua- 




1950 



1880 1890 1900 1910 1920 1930 1940 

From Pacific Southwest Field Committee (1955). 

Figure 6. Graph showing trends of mineral production in northwestern California during the period 1880-1953 



64 



California Division of Mines 



[Bull. 179 



tion of the faults along Redwood Mountain, along the 
largest belt of schist that lies west of the Klamath Moun- 
tains province. As shown on the geologic map (pi. 1), 
however, the southeastward continuation of the fault 
along the serpentine ridge is east of the faults that bound 
the Redwood Mountain belt of schist. Maxson (193 3, p. 
137) states that the rocks on the east side of the fault 
have been uplifted 400 feet relative to those on the west. 
It is likely that the estimate of the magnitude of uplift 
was based on physiographic data. Maxson (1933, p. 137) 
postulated a third fault to outline the area of Cenozoic 
rocks of the Crescent City platform. 

Cater and Wells (1954, p. 106) state that in the 
Gasquet quadrangle the structure is one of " . . . close 
overturned folds and high-angle reverse faults. The 
axial planes of the folds and the associated faults are 
roughly parallel, trend north-northeast, and dip steeply 
eastward. Other faults, some trending northeastward 
and others northwestward, postdate the folds and reverse 
faults but probably belong in general to the same period 
of deformation." They consider that this deformation 
resulted from the Nevadan disturbance at the close of the 
Jurassic period, but that differential vertical movements 
and gentle tilting probably began in late Miocene and 
are still continuing. 



o 80 



/ \ Combined lode ond plocer gold 



\t.\ 

:i 'I 



n 







/ i 



Lode gold 




'(! Placer gold 



1900 1910 1920 1930 1940 1950 

From Pocific Southwest Field Committee (1955) 

Figure 7. Graph showing production of gold in northwestern 
California during the period 1903-1953. 



MINERAL COMMODITIES 

Mining activity began in the report area during the 
middle 1800's and by 1958 mineral products having a 
total value of approximately $150,000,000 had been pro- 
duced. The chief interest in the early days was the gold- 
bearing placers along the Klamath River and its tributar- 
ies, but as prospecting diversified, significant quantities 
of other metallic mineral commodities such as chromite, 
quicksilver, copper, and manganese ores were produced. 
As the population of the area increased, production of 
nonmetallic mineral commodities such as sand and gravel 
increased to a point where their value exceeds that of 
the metallic mineral commodities. The combined produc- 
tion of metallic and nonmetallic mineral commodities has 
fluctuated markedly owing to various economic condi- 
tions (fig. 6). Although the total production of mineral 
commodities is small as compared to many areas of com- 
parable size in the western United States, it has con- 
tributed significantly to the development and economy 
of northwestern California. 

Gold 

Nearly all of the gold deposits in northwestern Cali- 
fornia are in the Klamath Mountains province, and this 
province ranks second only to the Sierra Nevada in gold 
production in California. The gold has come from both 
placer and lode deposits; placer deposits have been by far 
the most productive (fig. 7). Gold was the first metal 
diligently sought in the area. It is said to have been dis- 
covered by a Major Reading in 1848, in a placer deposit 
along the Trinity River near Douglas City. Within a 
few years, lode deposits of gold also were discovered. 



Most of the richer placer and lode deposits of gold had 
been found by the late 1800's. 

Production of gold from northwestern California dur- 
ing the period 1880-1952 totaled 3,852,800 fine ounces 
valued at $90,803,000 and during the year 1953 was 9,579 
fine ounces valued at $335,265. Production figures re- 
lated to type of deposit are not available prior to 1903, 
but during the period 1903-1952 approximately 1,602,000 
fine ounces of gold was produced from placer deposits, 
compared to 383,300 fine ounces of gold produced from 
lode deposits during the same period. In 1953 the gold 
production was 5,806 ounces from placer deposits, com- 
pared to 3,773 ounces from lode deposits during the same 
year. 

According to the report of the Pacific Southwest Field 
Committee (1955, p. 19-20), "Gold production reached 
its peak during the period 1937 through 1942, prior to 
interruption of mining during World War II. An increase 
in the price of gold from $20.67 to $35.00 per ounce in 
1934 greatly stimulated the gold mining industry in 
[northwestern California]. By 1943, however, the rising 
tendency of wages, the movement of miners into defense 
industries and the armed forces, shortages of equipment 
and supplies, plus Government restrictions including 
War Production Board Order L-208, forced most of the 
gold mines to close, although some of the larger placer 
mines were able to continue working. In July 1945, Gov- 
ernment restrictions on nonessential industries, including 
gold mining, were lifted; but most of the machinery and 
equipment used in placer mining had been transferred to 
war industries, underground workings had deteriorated, 
and operating costs had risen. Contributing to the decline 



l'M()| 



124' 



Northern (ihm Ranges \m> Klamath Mountains 

123° 



65 




Area of granitic rocks 



LODE GOLD DEPOSITS 



@) More than 1500,000 production 

® 8100,000 to 8 500,000 production 

• Less than 8 100,000 production 

o No recorded production 



PRINCIPAL PRODUCERS 



No 

1 


MINE 
Hazel 






Production 
8 800,000 


2 


Golden Eagle 


(Sheba) 


1,000,000 


3 


Dewey 






900,000 


4 


Highland 1 






500,000 


5 


Block Bear 






3,000,000 


6 


Klamath 






600,000 


7 


Cummings (Oro Grande) 


500,000 


8 


Gilta (Gold H 


II) 




1,000,000 


9 


Headlight 






500,000 


10 


Trinity Bonanza K 


ng 


1,250,000 


1 1 


Enterprise 






500,000 


12 


Alaska group 






600,000 


13 


Fair view 






5,000,000 


14 


Brown Bear 






10,000,000 


15 


Venecia 






500,000 


16 


Midas 






3,500,000 


17 


Siskon 




not 


re ported 



SA 



Modified after Pacific Sout 
Field Committee (1955 ) 



40 MILES 



Figure 8. Map of northwestern California showing location of lode deposits of gold. 



3 — 18730 



66 



California Division of Mines 



[Bull. 179 



Area of granitic rock 

• Placer gold deposit 

O Placer platinum and 
gold deposit 




Modified after Pocific Southwest 
Field Committee (19551 



Figure 9. Map of northwestern California showing location of placer deposits of gold and platinum. 



I960] 



\ [-hern Coasi Ranges wd Klamath Mountains 



67 



in gold production was the depletion of some important 
placer areas and deposits of high grade ore". 

Lode deposits of gold I Eg. 8) occur in all of the prin- 
cipal formations of middle Late Jurassic and older ages 
in the Klamath Mountains province. Granitic rocks of 
Late furassic age intrude all of these formations, and the 
gold probably is related to them although few of the 
deposits are iii granitic rocks. The rocks of the northern 
Coast Ranges are younger than the granitic rocks of the 
Klamath Mountains, and lode deposits of gold in them 
are rare. 

Production of gold from lode deposits has come chiefly 
from the pre-Jurassic rocks of the Klamath Mountains 
arc; quartz veins containing native gold in the Bragdon 
formation have been the most important source. Seven- 
teen mines have produced more than S500.000 in gold, 
and several have produced more than f 1,000,000 in gold. 
The greatest production has been from the Brown Bear 
mine, where gold valued at as much as $10,000,000 is 
said to have been produced (Averill. 1933, p. L3). Many 
of the mines have been described by Ferguson (1914), 
Tucker (1922a), Averill (1931, 1933), Maxson (1933), 
and others. 

The placer deposits of gold (fig. 9) arc the products of 
erosion, transportation and gravitational concentration 
of the gold of the lode deposits of the Klamath Moun- 
tains province. Detrital gold occurs in most of the sedi- 
mentary formations of Tertiary and Quaternary ages in 
the Klamath Mountains, as the placer gold ultimately was 
derived from the rocks of Late Jurassic and older ages 
that contained the gold-bearing lode deposits. The richer 
placer deposits of gold, however, arc those of Quaternary 
age. that is. the gravels in the terraces and stream beds 
along the courses of the present streams. In general, this 
is the result of repeated re-concentration of detrital gold 
from volumes of sedimentary rocks of Tertiary and 
Quaternary ages as they were eroded, but also added to 
each cycle was gold derived directly from the erosion of 
gold-bearing lodes. 

The placer deposits arc greatest in number in the areas 
of most abundant lode deposits of gold and along the 
courses of the major streams that drain those areas (com- 
pare figs, s and 9). Thus the placer deposits are more 
widespread than the related lode deposits, and although 
most ot them are in the Klamath Mountains province, a 
few occur in the northern Coast Ranges. In addition, 
sediments that reached the ocean have been winnowed to 
form deposits in beach sands along the coast of northern 
Humboldt and Del Norte Counties. Much of the gold in 
the beach sands probably was derived from erosion of 
sedimentary rocks of Tertian- and Quaternary ages that 
occur nearby. The gold in the beach sands, however, is 
finely divided, and in general is of little economic in- 
terest. 

The occurrence of gold-bearing gravels in the Trinitv 
River basin is described by Dillcr (1911 and 1914a) with 
regard to several cycles of erosion, and the distribution 
of the principal areas of gold-bearing gravels along the 



major streams of northwestern California is described in 
detail bj Halej (1923, p. 82-101). Attempts to mine the 
beach deposits are described b\ Logan ( L919, p. 41-43). 
In the northern Coast Ranges of California, lode and 
stream placer deposits of gold have been found at a few- 
places, but they have been of slight economic interest. 
Small quantities of gold are associated with cinnabar at 
some quicksilver mines and in detrital deposits nearby 
(E. H. Bailey, oral communication, 1956). Panning in 
several streams in the northern Coast Ranges has yielded 
traces of gold, but important concentrations have not 
been found. Logan (1919, p. 44-48) describes two inter- 
esting localities in Mendocino County, one near I Iopland 
and the other near Capclla, where small quantities of 
detrital gold associated with platinum and cinnabar were 
produced. Gold-bearing stringers of quart/ in metamor- 
phosed rocks of the Franciscan formation(?) arc noted 
by O'Brien (1953, p. 359-360). 

Platinum 

Detrital platinum occurs in many of the gold-bearing 
placer deposits in northwestern California (U<j:. 9). It 
has been recovered only as a by-product of placer mining 
for gold, as deposits sufficiently rich to be mined only 
for platinum have not been found. Although the platinum 
occurs in the same placer deposits as the gold, it is 
thought likely to have been eroded from bodies of ultra- 
mafic rocks (Logan, 1919, p. 10) rather than from the 
lode deposits from which the gold was derived. The 
platinum-bearing placer deposits of northwestern Cali- 
fornia are described by I.ogan (1919; also see Day and 
Richards. 1906). 

The production of platinum that was recorded during 
the period 1 S80-1952 was approximately 1,850 ounces 
valued at 5129,200, but none was recorded in 1953. The 
production figures, however, do not accurately reflect 
the amount of platinum that has been mined, as much 
platinum is said to have been discarded during the early 
days of mining. 

Chromite 

Deposits of chromite have been mined in both the 
Klamath Mountains and the northern Coast Ranges (fig. 
Hi). Chromite was discovered in Del Norte Count \ prior 
to the Civil War. and during the period 1869-1873 about 
1,500 tons of ore was shipped annually from Crescent 
Cit) (Maxson. 1933, p. 149). In the twentieth century, 
however, the mining of chromite has been chiefly a war- 
time or defense activity, and the peaks of production 
were during the periods 1917-1920 and 1941-1945. \ 
smaller production peak during the period 1951-1955 re- 
sulted from subsidy under a Federal Government stock- 
piling plan. 

\ccurate production figures arc not available for much 
of the period during which chromite was mined. How- 
ever, the approximate total production of chromite from 
northwestern California, through 1955, is about 190.0(H) 
long tons of lump ore and concentrates, with an esti- 
mated average Cr 2 3 content of about 45 percent. Two- 
thirds of this production has come from Del Norte and 



68 



California Division of Mines 



I Bull. 179 



124 



EX PLANATION 



Principol areas of 
ultramafic rocks 



CHROMITE DEPOSITS 

(•) Producer, more than IOOO Ions 
• Producer, less than IOOO tons 
° No recorded production 




Modified after Pacific Southwest 
Field Committee (1955) 



Figure 10. .Map of northwestern California showing location of deposits of chr 



I960] 



Northern Coasi Ranges vnd Klamath Mountains 



69 



Siskiyou Counties, while approximately 90 percent of the 
remaining production has come from Glenn and rehama 
Counties. Production from Del Norte County has been 
more rh:m double that from any other county. Glenn 
Counrv ranks second in production, followed closely by 
Siskiyou County. 

The mineral chromite is the only important com- 
mercial source of chromium. Chromite ore occurs only 
in the bodies of ultramafic rocks or in placer deposits 
resulting from their erosion. Most commonly the chro- 
mite occurs in dunite as small grains scattered throughout 
the rock. Where the grains of chromite are sufficiently 
abundant to be of economic interest the rock is referred 
to as disseminated ore. Less commonly, the chromite 
occurs as stringers, pods, and lenses in the ultramafic 
rocks, and these masses are referred to as lump or high- 
grade ore. Mineable bodies of disseminated ore may range 
from a few hundred pounds to as much as 100,000 tons 
of ore containing at least 25 percent chromite, whereas 
bodies of lump ore may range from less than a ton to 
10,000 tons (Wells, Cater, and Rynearson, 1946, p. 
12-13). Placer deposits of chromite have been formed 
by erosion of the ultramafic rocks and reconcentration 
of the heavy minerals, bur with few exceptions they are 
of little economic importance. In the past, how ever, lump 
ore that has been eroded from pods and lenses in the 
ultramafic rock, and that has traveled only short dist- 
ances down hillsides, was recovered in significant quan- 
tities. 

In Del Norte County, "1 chromite deposits have been 
worked, and the production lias been chiefly lump ore. 
The total quantity of ore shipped from individual de- 
posits by 1950 ranged from 5 to 20,000 long tons; two 
deposits yielded more than 10,000 long tons, a third more 
than 5,000, and a fourth more than 3,000 (Wells, Cater, 
and Rynearson, 1946, p. 3). In Siskiyou County, 89 
chromite deposits yielded quantities of ore ranging from 
a few long tons to a maximum of 4.000 long tons, and 
approximately a third of the production was disseminated 
ore (Wells and Cater, 1950, p. 79, 97; also see Wells, 
Smith, Rynearson, and Livermore, 1949). Disseminated 
ore accounts for nearly the total production of chromite 
from Glenn County, the county second in chromite pro- 
duction in northwestern California, and came chiefly 
from one group of deposits (Dow and Thayer, 1946, p. 
9-10). Production from Tehama County also has been 
mainly disseminated ore, and chiefly from one group of 
deposits (Rynearson, 1946, p. 200). 

The known reserves arc almost entirely restricted to 
deposits of disseminated ore, for deposits of lump ore 
usually are mined out shortly after their discovery. In 
Del Norte County, therefore, reserves have not been 
estimated, as the mining has been chiefly for lump ore. 
However, beach sands at a locality near Crescent City 
are reported to contain an average of 7 percent CroO :! and 
are estimated to constitute a deposit of at least 500,000 
cubic yards (Wells, Cater, and Rynearson, 1946, p. 75- 
76). Indicated and inferred reserves of disseminated ore 



in Siskiyou County are 274,000 short tons with an average 
grade of 8 percent Cr 2 3 (Wells and Cater, L950, p. 97- 
98). Reserves in the northern (."oast Ranges, with the ex- 
ception of those in Tehama County, consist of dissemi- 
nated ore occurring chiefly in Glenn County, atul include 
4.000 long tons averaging 20 percent Cr 2 3 , 29,000 tons 
averaging 12 to 13 percent CroO :; , and 12,000 tons aver- 
aging 6 percent Cr L .(). (Dow and Thayer, 1946, p. 8). 
Know n reserves in Tehama County arc 109,000 short tons 
of disseminated ore averaging about 10 percent Cr () ; . 
ami 4,060 tons of lump ore averaging about 4^~ percent 
Cr.O :; (Rynearson, 1946, p. 204, tabic- 1"). It is doubtful 
that much of these reserves has been mined since Ry- 
nearson's report. 

According to the report of the Pacific Southwest Field 
Committee (1955, p. 24), "Most of the production of 
chromite from northern California has been from small 
high-grade deposits, which yield ore that can be sorted 
by hand for shipping to distant points. Such high-grade 
pods are rapidly depicted, and the discover) of many 
more virgin outcrops of such ore cannot be expected. As 
underground exploration for concealed bodies of chrom- 
ite is nearly on a hit-or-miss basis, it seems unlikely that 
production from deposits of this type can be maintained 
at the prevailing rate for many years. Deposits of dis- 
seminated chromite arc becoming of increasing interest, 
and although they arc much lower in grade than the 
small high-grade type, they contain in the aggregate far 
more chromite. Ore from deposits of the disseminated 
type, in contrast to the more easily handled high-grade 
ore, must be milled at or near the deposit before being 
shipped. It is only from the disseminated deposits, or, less 
likely, from a radical improvement in technique for the 
discovery of high-grade deposits, that a dependable pro- 
duction of chromite may be expected on a long-term 
basis". 

Copper 

In northwestern California. 174 copper deposits have 
been reported, but few have creditable production 
records. It does not rank high among the well-known 
copper producing areas of California, although Siskiyou 
Counts ranked first during the brief period 1943-1945. 
The total recorded production of copper from north- 
western California during the period 1880-1952 is 
41,468,000 pounds. Peaks of production were during the 
periods 1915-1930 and 1943-1945. Copper was not pro- 
duced in the area during 1953. Zinc is contained in some 
of the copper ores, but there is no record of zinc con- 
centrates having been produced in the area. The princi- 
pal by-products of the mining of copper ores have been 
gold and silver. 

The copper occurs in complex sulfide ores. All of the 
deposits having significant production are in the Klamath 
Mountains, with the exception of the Island Mountain 
mine in the Coast Ranges (fig. 11). The most productive 
deposits in the Klamath Mountains are lenses and dis- 
seminated grains of copper-sulfide minerals in schist of 
low metamorphic grade. .Many smaller deposits, however, 



70 



California Division of Mines 



[Bull. 179 



UE LEDGE 



COPPER DEPOSITS 
(•) Producer, more than 1,000,000 lbs 
• Producer, less than 1,000,000 lbs 
° Prospect, no recorded production 




Modified chiefly offer Economic Mineral 
Map Number 6 (COPPER), California Div 
of Mines, Bull. 144, 1948 



Figure 11. Map of northwestern California showing location of deposits of copper. 



I960] 



Northern Gi\m Ranges vnd Klamath Mountains 



are in or adjacent to bodies of ultramafic rocks, and some 

are in quartz veins. The Island .Mountain deposit is at 
least partly a replacement of the graywacke and con- 
glomerate of the Franciscan formation by pvrrhotite and 
chalcopyrite. 

The principal mines in the report area in the Klamath 
Mountains province are the Gray Eagle and Blue Ledge, 
both having produced more than 1,000,000 pounds of 
copper (Eric, 1948, p. 341, 343). Several others have 
produced between 100,000 and 1,000,000 pounds of 
copper. The only significant production from the 
northern Coast Ranges has come from the Islam! Moun- 
tain mine. According to Stinson (1957, p. 18), nearly 
9,000,000 pounds of copper were produced from 132,000 
tons of ore shipped from the Island Mountain mine dur- 
ing its period of operation (1915-1930), the ore averag- 
ing about 3.3 percent copper, 1.1 ounces of silver, and 
0.07 ounces of gold, per ton. 

No reliable estimate of reserves of copper is available, 
but a relatively large tonnage remains in some of the 
larger mines as pillars and marginal ore. Recent geo- 
physical work by the U. S. Geological Survey indicates 
that a substantial quantity of ore may yet remain at the 
Island Mountain mine (in Stinson, 1957, p. 31). Small 
reserves of ore recently have been developed at the 
Copper Bluff mine near Hoopa. 

Silver 

A small amount of silver has been produced from 
northwestern California, chiefly as a by-product of the 
mining for gold, copper, and to a lesser extent, lead. A 
few deposits have been worked chiefly for silver 
(Tucker. 1922b). The recorded production of silver dur- 
ing the period 1880-1952 is approximately 685,000 
ounces. From 1903 through 1952 the recorded produc- 
tion of silver was 531,700 ounces, of which about 63 
percent came from lode deposits and the remaining from 
placer deposits. Xo breakdown for years prior to 1903 
is available. Production in 1953 was 2,730 ounces of 
silver, of which about 78 percent came from lode de- 
posits. Reserves of silver ore are not known in north- 
western California, and future production probably will 
depend on the recover)- of silver as a by-product from 
ores of other metals. 

Quicksilver 

Deposits of quicksilver occur in both the Klamath 
Mountains and northern Coast Ranges. Most of the pro- 
duction, which amounts to approximately 245,000 flasks 
of quicksilver, has come from the Sulfur Bank (Everhart. 
1946), Abbott (Averill, 1947), Altoona (Ransome and 
Kellogg, 1939), and Cloverdale and Culver Baer mines 
(Bailey, 1946). All of these mines are in the northern 
Coast Ranges with the exception of the Altoona. The 
Cloverdale and Culver Baer mines are in the western tip 
of the Mayacmas district, which extends southeastward 
beyond the report area. Production from the Mayacmas 
district alone has been 500,000 flasks of quicksilver. 

The quicksilver occurs chiefly as cinnabar. Most of 
the deposits of cinnabar are in or near bodies of ultra- 



mafic rocks, and those of the northern Coast Ranges are 
general!) in the central belt of the Franciscan formation 
(fig. 12). The deposit at Sulfur Bank mine is unusual, 
as it is chiefly in volcanic and lacustrine deposits of 
Quaternary age that overlie rocks of the Franciscan for- 
mation. 

Long-term reserves of quicksilver-bearing ore gener- 
ally arc not developed, because the ore bodies usually 
are small and irregular and arc mined as they are en- 
countered. In the known districts additional ore bodies 
doubtless will be discovered during periods of demand 
that warrant the expense of exploration. Also, deposits 
beyond the known districts may be discovered, as pan- 
ning of stream gravels by members of the U. S. Geo- 
logical Survey indicates that cinnabar is more w idely dis- 
tributed in the area than is suggested by the distribution 
of the known deposits. 

Manganese 

Most of the production of manganese ore from 
northwestern California has come from deposits in the 
northern Coast Ranges, although many deposits also are 
known in the Klamath Mountains (rig. 13). Of the nearly 
2<ih mines and prospects in the area, only seven mines 
have a recorded production of more than 1,000 tons of 
manganese ore, and all seven are in the northern Coast 
Ranges. The greatest recorded production of manganese 
ore from a single mine is about 5,000 long tons. The min- 
ing of manganese ore has been sporadic, and much of the 
production has resulted from wartime demand and Fed- 
eral Government purchases that provided relatively high 
market prices. The total recorded production of man- 
ganese ore from northwestern California during the 
period 1880-1952 is about 37,000 long tons, and during 
1952 the recorded production was 1,052 long tons. 

Nearly all of the manganese deposits are associated 
with chert, and those of the northern Coast Ranges are 
chiefly in chert of the Franciscan formation. The de- 
posits have been described by Trask. Wilson, and Simons 
(1943). The higher quality manganese deposits are of the 
oxide minerals that occur near the surface and extend 
downward only short distances. This occurrence of ore 
makes for small reserves, and such deposits are rapidly 
depleted. The principal reserves of manganese are con- 
tained in the carbonate or silicate ores that underlie the 
oxide ores and extend to greater depths. These reserves, 
however, are low in grade and require benefication to be 
commercial. Thev also are not readily amenable to 
mechanical concentration, and only a few shippers have 
been able to meet the specifications of metallurgical 
manganese ores. 

Miscellaneous Metalliferous Commodities 

Deposits of antimony, iron, molybdenum, lead, nickel, 
and tin have been reported in northwestern California 
(fig. 14), and small quantities of the ores of some of 
these metals have been produced. The total value of 
their production, however, is negligible from a regional 
viewpoint, and with the exception of nickel there is little 



72 



California Division of Mines 



[Bull. 179 



124 



123° 




QUICKSILVER DEPOSITS 

(J) Large production 
• Smoll production 
o No recorded production 



Modified chiefly after Economic 
Mineral Mop No.l — Quicksilver, 
Coliforma Div. of Mines, 1937. 



Figure 12. Map of northwestern California showing location of deposits of quicksilver. 



I960] 



Northern Coasi Ranges \m> Klamath Mountains 



73 



124 



123° 




MANGANESE DEPOSITS 

® Production more than 1000 tons 
• Production less than 1000 tons 
o No recorded production 



SONOMA 



Modified chiefly after Economic 
Mineral Map Number 5 (Manganese) 
California Div. of Mines, Bull 125,1943 



40 MILES 



Figure 13. Map of northwestern California showing location of deposits of manganese. 



"4 



California Division of Mines 

123° 



[Bull. 179 




EXPLANATION 

.a. Antimony 

A Arsenic 

A Asbestos 

C Clay 

G Graphite 

• Iron 

9 Lead-silver 

M Magnesite 

■ Molybdenum 

n Nickel 

(D Ocher 

o Soapstone, talc 

▼ Tin 

MA " Tungsten 

A Volcanic ash 



Modified after Pacific Southwest 
Field Committee 1955 



Figure 14. 



Map of northwestern California showing location of deposits of miscellaneous mineral 

commodities. 



I960 



Northern Coasi Ranges vnd Klamath Mountains 



75 



indication that production of these metals will prove im- 
portant to the economy <>t the area. 

Significant quantities of nickel ore currently are being 
mined in southwestern Oregon, in areas where old-hind 

surfaces are formed on bodies of ultramafic rocks. On 
these old surfaces, which arc presumably parts of the 
Klamath peneplain of Diller, lateritic 'soil has been 
formed, and where the soil is formed on bodies ot ultra- 
malic rocks, both the soil and underl) ing weathered rock 
is enriched with nickel. Similar old-land surfaces also 
are formed on ultramafic rocks in northwestern Cali- 
fornia, chiefly in Del Norte County, and several major 
metal-mining companies were investigating the nickel- 
producing potential of the area in 1957. 

Nonmetallic Mineral Commodities 

The dollar value of nonmetallic mineral commodities 
produced in the northern Coast Ranges is many times 
greater than that of metallic commodities, but in the 
Klamath Mountains it is only a third that of metallic 
commodities. The nonmetallic commodities generally are 
of low unit value compared to metallic commodities, ami 
with the exception of the mineral fuels, they are used 
chiefly for construction purposes. In most cases the 
source of supply must of necessity be near the consumer. 

Miscellaneous stone, including sand, gravel, crushed 
rock, rubble, and riprap, is by far the most important 
nonmetallic mineral commodity. During 1953 it consti- 
tuted nearly half of the dollar value of the total mineral 
production of northwestern California. Its production, 
transportation, and use in roads, ballast, fills, and con- 
crete construction have resulted in the employment of 
such substantial numbers of persons as to be of great 
economic importance to the area. 

Sand and gravel arc obtained from river, terrace, and 
beach deposits, and the resources of such material are 
large. Greenstone and chert are widely used as road 
metal on secondary roads, particularly in the Coast 
Range, and deposits of these rocks arc so abundant and 
widespread in areas of the Franciscan formation as to 
be practically inexhaustible. Blocks of graywacke com- 
monly have been used as riprap, but glaucophane schist 
is becoming of increasing interest for this use. Although 
production of miscellaneous stone may vary consider- 
ably over periods of time, a steady increase in population, 
industrial expansion, road and dam construction, and 
many other factors will doubtless result in increased pro- 
duction. 

Deposits of limestone occur at many places in north- 
western California (fig. 15), but the most important from 
an economic standpoint are the larger of the Paleozoic 
and Triassic deposits in the Klamath .Mountains. The 
foraminiferal limestone of the Franciscan formation in 
the northern Coast Ranges generally occurs as deposits 
too small to be of economic interest. Many of the lime- 
stone deposits of northwestern California have been tabu- 
lated and described briefly' by Logan (1947) and others, 
and those near Gazelle in Siskiyou County have been 
studied in detail by Heyl and Walker (1949). Several 



of the deposits have had a small production, mainl) for 
agricultural uses and the manufacture of quicklime, and 
a small quantity of recrystallized limestone has been 
quarried as marble for dimension stone; some are thought 
to be suitable for the manufacture of cement. The last 
recorded production of limestone in the area was in 
L945, and significant future production probably will 
await increased population and industrial expansion. 

Many other nonmetallic commodities haw been mined, 
but have not yet proved of great importance to the 
economy of the area. Clay has been mined, principally 
in the vicinit) of Eureka, for the manufacture ot brick 
and tile, and other deposits having small production are 
near Scott Valley. The total recorded production of 
Clay has amounted to about $337,000. Dimension stone. 
including sandstone and granite, has been mined, but 
little has been produced during the past few decades. 
Deposits of asbestos occur at some places in areas of ultra- 
mafic rocks, but none has had appreciable production. 
Other nonmetallic mineral commodities that have been 
produced in small quantities in northwestern California 
include volcanic rocks for use as light-weight construc- 
tion aggregate, pebbles for use in grinding nulls, mag- 
nesite, sulfur, ami semiprecious gem stones. 

Gas and Oil 

Wells have been drilled for gas and oil in the northern 
Coast Ranges, chiefly in the Point Arena, Mattole River, 
Bear River, and Tompkins Hill areas (see fig. 16). A few 
of the wells have yielded significant quantities of gas 
but none has yielded more than minor amounts of oil. 
In general, the results of the drilling have been disap- 
pointing, but several oil companies were continuing ex- 
ploration in 1956. 

1 he only production of gas and oil has been from 
western Humboldt Countv. A minor quantity of gas was 
withdrawn for local consumption near Bnceland during 
the period 1909-1938, but the greatest production has 
been from the Tompkins Hill field near Fortuna. A small 
quantity of oil was produced near Petrolia in 1953, the 
first recorded production of oil in the area. 

According to a report of the Pacific Southwest field 
Committee < 1955, p. 35), "The value of petroleum and 
natural gas produced in [northwestern California! has 
been about 1 percent of the total value of the basin's 
mineral production. The production of oil and gas in 
| northwestern Californial. however, has been fairly re- 
cent, and the combined values of petroleum and natural 
gas extracted in 1953 amounted to 12 percent of the 
value of [northwestern California! mineral production 
of that year. For the years 1909 through 1952 the annual 
average volume of natural gas withdrawn and utilized 
was about 41 v 100,000 cubic feet, compared with the 
withdrawal of 1,768,197,000 cubic feet in 1953. The trend 
of the natural gas production in the area since 1939 has 
been one of gradual ascendancy". 

In the northern Coast Ranges the rocks of principal 
interest from the standpoint of gas and oil production 
are Miocene and Pliocene in age, and of these the rocks 



76 



California Division ok Mines 



[Bull. 179 




LIMESTONE DEPOSITS 
• Smoll recorded production 
o No recorded production 



Modified after Pacific 

Southwest Field Committee 

(1955) 



40 MILES 



Figure 15. Map of northwestern California showing location of deposits of limestone. 



1960| 



124 



Northern Coast Ranges vnd Klamath Mountains 

123° 



77 




EXPLANATION 

Principol oreos underlain by 
monne sedimentary rocks 
of Tertiary age. 

COAL DEPOSITS 
Small production 
• No recorded production 



o Exploratory well drilled 
for oil and gas, exclusive 
of the Sacramento Volley 



Location of coat deposits 
modified otter Pacific 
Southwest Field Committee 
(1955) 



Location of exploratory 
wells after Jennings 
and Hart (19561 



40 MILES 
1 



Figure 16. Map of northwestern California showirg location of deposits of coal, and location of wells 
drilled for oil and gas (exclusive of the Sacramento Valley). 



78 



California Division of Minis 



Bull. 179 



of Pliocene age have been the most productive. The larg- 
est and most productive area of rocks of Pliocene age is 
the Eel River Valley in west-central Humboldt County 
where west-trending folds provide structural traps for 
the accumulation of gas and oil. Westerly structural 
trends, in addition to meager data resulting from marine 
dred^ino-, suggest that offshore from some of the coastal 
areas^ rocks of interest from the standpoint of gas and 
oil may be of considerable extent. 

According to a report of the Pacific Southwest Field 
Committee (1955, p. 36), "The Tompkins Hill gas held 
near Fortuna was discovered in 1937, and is the only 
commercially productive area at present. Nine wells were 
completed to the end of 1953. During 1953 about 
1 768 197 000 cubic feet of gas was produced. The total 
production of the field to the end of 1953 was 12,703,- 
000 000 cubic feet of gas. The California Department of 
Natural Resources, Division of Oil and Gas, estimated 
die reserve of this field to be about 20,000,000,000 cubic 
feet of "as as of July 1, 1954. The field is on a small anti- 
cline on the northeast limb of the Eel River synclme. 
The gas is produced from sands of Pliocene age at a 
depth" of approximately 5,000 feet". 

Coal 

Small quantities of coal have been mined at several 
localities in northwestern California (see fig. 16), chiefly 
from strata of Tertiary age. The coal ranges from lignite 
to sub-bituminous in rank. The recorded production of 
coal during the period 1880-1952 was approximately 
4 000 tons," and most of the production was prior to 
1925. Production was chiefly from deposits near Dos Rios 
in Mendocino Countv, and at Big Bar and Browns Creek 
(photo 11) in Trinity County. Coal is not now produced. 

REFERENCES CITED 

Mien I F., and Baldwin. E. M., 1944, Geology and coal resources 

' of the Coos Bay quadrangle. Oregon: Oreg. Dept. Geol. and 
Min. Industries, Bull. 27, 154 p. 

\nderson C A 1936, Volcanic history of the Clear Lake area, 

' California: Geol. Soc. America Bull., v. 47, no. 5, p. 629-644. 

Anderson, C. A., and Russell, R. D., 1940. Ternary formations of 
northern Sacramento Valley, in 35th report of the State Miner- 
alogist: California Div. Mines, v. 35, no. 3, p. 219-2*3 

Anderson F. M., 1933, Knoxville-Shasta succession m California: 
Geol. Soc. America Bull., v. 44, no. 12, p. 1237-1270. 

t 1938, Lower Cretaceous deposits in California and Oregon: 

Geol. Soc'. America Special Paper 16, 339 p. 

1945, Knoxville series in the California Mesozoic: Geol. 

Soc. 'America Bull., v. 56, p. 909-1014. 
Werill, C. V., 1931, Preliminary report on economic geology of 
the Shasta quadrangle, in 27th report of the State Mineralogist: 
California Div. Mines, v. 27, no. 1, p. 3-65. 

, 1933. Gold deposits of the Redding and YVeaverville quad- 
rangles, in 29th report of the State Mineralogist: California Div. 
Mines, v. 29, nos. 1, 2, p. 2-73. 

t 1941, Mineral resources of Humboldt County, in 37th 

report of the State Mineralogist: California Div. Mines, v. 37, 
no. 4, p. 499-528. 

, 1947, Mines and mineral resources of Lake County, Cali- 
fornia: California Jour. Mines and Geology, v. 43, no. 1, p. 15-40. 

Averitt, Paul, 1945, Quicksilver deposits of the Knoxville district, 
Napa, Yolo, and Lake Counties, California: California Jour. 
Mines and Geology, v. 41, no. 2, p. 65-89. 



Bailey, E. H., 1946, Quicksilver deposits of the western Mayacmas 
district, Sonoma County, California, in 42nd report of the State 
Mineralogist: California Div. Mines, v. 42, no. 3, p. 199-230. 

Bailey, E. H., and Irwin, W. P., 1959, K-feldspar content of 
Jurassic and Cretaceous graywackes of the northern Coast 
Ranges and Sacramento Valley, California: Am. Assoc. Petro- 
leum Geologists Bull., v. 43, no. 12, p. 2797-2809. 

Becker, G. F., 1888, Geology of the quicksilver deposits of the 
Pacific slope: U. S. Geol. Survey Mon. 13, 219 p. 

Brewer, W. A., Ill, 1954, The geology of a portion of the China 
Mountain quadrangle, California: University of California mas- 
ter's thesis. 

Brice, J. C, 1953, Geology of Lower Lake quadrangle, California: 
California Div. Mines Bull. 166, 72 p. 

Cater, F. W, Jr., and Wells, F. G., 1954, Geology and mineral 
resources of the Gasquet quadrangle, California-Oregon: U. S. 
Geol. Survey Bull. 995-C, p. 79-133. 

Chesterman, C. YV., 1952, Nephrite and associated rocks at Leech 
Lake Mountain, Mendocino County, California (abs.) : Geol. 
Soc. America Bull., v. 63, no. 12, pt. 2, p. 1323. 

Church, C. C, 1952, Cretaceous foraminifcra from the Franciscan 
Calera limestone of California: Cushman Found. Foram. Re- 
search Contr., v. 3, pt. 2, p. 68. 

Clark, S. G., 1940, Geology of the Covelo district, Mendocino 
County, California: California Univ., Dept. Geol. Sci. Bull., 
v. 25, no. 2, p. 119-142. 

Cushman, J. A., and Todd, M. R., 1948, A foraminifera fauna from 
the New Almaden district, California: Cushman Lab. Foram. 
Research Contr., v. 24, pt. 4, p. 90-98. 

Davis, W. M., 1933, The lakes of California, in 29th report of the 
State Mineralogist: California Div. Mines, v. 29, nos. 1, 2, p. 
175-236. 

Day, D. T., and Richards, R. H., 1906, Useful minerals in the 
black sands of the Pacific slope, in Mineral resources of the 
United States: U. S. Geol. Survey, p. 1175-1258. 

Dickerson, R. E., 1922, Tertiary and Quaternary history of the 
Petaluma, Point Reyes, and Santa Rosa quadrangles, California: 
California Acad. Sci. Proc, ser. 4, v. 11, no. 19, p. 527-601. 

Diller, J. S., 1894a, Revolution in the topography of the Pacific- 
Coast since the auriferous gravel period: Jour. Geologv, v. 2, 
p. 32-54. 

— , 1894b, Tertiary revolution in the topography of the Pacific 
Coast: U. S. Geol. Survey 14th Ann. Rept., pt. 2, p. 397-454. 

Diller. J. S., 1898, Description of the Roseburg quadrangle: U. S. 
Geol. Survey Geol. Atlas, Folio 49, 4 p. 

, 1902, Topographic development of the Klamath Moun- 
tains: U. S. Geol. Survey Bull. 196, 69 p. 

— , 1903a, Klamath Mountain section: Am. Jour. Sci., ser. 4, 
v. 15, p. 342-362. 

, 1905b, Description of the Port Orford quadrangle: U. S. 

Geol. Survey Geol. Atlas, Folio 89, 6 p. 

— , 1905, The Bragdon formation: Am. lour. Sci., ser. 4, v. 
19. p. 379-387. 

— , 1906, Description of the Redding quadrangle: U. S. Geol. 
Survey Atlas, Folio 138, 14 p. 

— , 1907, The Mesozoic sediments of southwestern Oregon: 
Am. Jour. Sci., ser. 4. v. 23, p. 401-421. 

— , 1908, Strata containing the Jurassic flora of Oregon: Geol. 
Soc. America Bull., v. 19. p. 367-402. 

— , 1911, The auriferous gravels of the Trinity River basin, 
California: U. S. Geol. Survey Bull. 470. p. 11-29. 

— , 1914, Auriferous gravels in the Weavervillc quadrangle. 
California: U. S. Geol. Survey Bull. 540, p. 11-21. 

— , 1915, The relief of our Pacific coast: Science, v. 41, p. 
48-57. 

, 1921, Chromite in the Klamath Mountains, California and 

Oregon: U. S. Geol. Survey Bull. 725. p. 1-35. 

Diller, J. S., and Kay, G. F., 1909, Mineral resources of the Grants 
Pass quadrangle and bordering districts, Oregon: U. S. Geol. 
Survey Bull. 380, p. 48-79. 

, 1924, Description of the Riddle quadrangle: U. S. Geol. 

Survey Geol. Atlas, Folio 218, 8 p. 



19601 



Northern Coasi Ranges vnd Klamath Mountains 



79 



Dow, I). II.. and Thayer, 1. P., 1946, Geological investigations 

of chromite in California: California Div. Mines Hull. 134, pt. 2, 

chap. 1, 38 p. 
Durham. J. W\. and Kirk, W. V., 1950, \ge of the Coralliocbama 

beds "t the Pacific (.'oast (abs.): Geol. Sue. America Bull., v. 

61, no. 12, |>f. 2, p. 1537. 
I ric, |. II., 1948, Tabulation of copper deposits of California, in 

Copper in California: California Div. Mines Hull. 144. p. 199-357. 
Everhart, I). I... 1946, Quicksilver deposits at the Sulfur Bank 

mine, lake County, California, in 42ml report of the State 

Mineralogist: California Div. Mines, v. 42. no. 2. p. 125-153. 
Fenneman, X. M., 1931, Physiography of western I nited States 

\e« York, McGraw-Hill Book Co., Inc., 534 p. 
Ferguson, II. G., 1914, Gold lodes of the Weaverville quadrangle, 

Californi i I . S. < leol. Survey Hull. 540. p. 22 
Gay, T. E., 1949, Geology of Upper Coffee Creek. Etna quad 

rangle, California: University of California master's thesis. 
Gealey, W. K.. 1951, Geology of the Healdsburg quadrangle, 

California: California Div. Mines Hull. 161, p. 7-50. 
Glaessner, M. I.. 1949, Forminifera of Franciscan (California): 

Am. Vssoc. Petroleum ( ieologists Bull., v. 33, no. 9, p. 1615-1617. 
Haley, C. S.. 1923, Gold placers of California: California State 

Mining Bur. Bull. 1 '2. 167 p. 
1 I.miia, G. I).. 1952, Geology of the continental slope off central 

California: California Acad. Sci. Proc, ser. 4. v. 2", no. 9, p. 

325-358. 
Hershey, O. II.. 1900, Vncient alpine glaciers of the Sierra Costa 

Mountains in California: Jour. Geology, v. 8, p. 42-57. 
, 1901, Metamorphic formations of northwestern California: 

Am. Geologist. \. 2~, p. 225-245. 
— , 1903a, Some evidence of two glacial stages in the Klamath 

Mountains in California: Am. Geologist, v. 31, p. 159-156. 
, 1903b, Structure of the southern portion of the Klamath 

Mountains, California: Am. Geologist, v. 31, p. 231-245. 
— , 1903c, The Sierran Valleys of the Klamath region, I ill 

fonua: Jour. Geology, v. 11. p. 155-165. 

. 1903d, The relation between certain river terraces and 

the glacial scries in northwestern California: Jour. Geology, 

v. 11, p. 451-458. 
, 1904, The Bragdon formation in northwestern California: 

Am. Geologist, v. >;, p. 248-256, 347-360. 
— , 19(16, Some western Klamath stratigraphy: Am. Jour. Sci., 

ser. 4, v. 21, p. 58-66. 

— , 1911, Del Xorte County geology: Min. and Sci. 

Press, v. 102, p. 468. 
Ileyl, (i. R., and Walker. G. W'., 1949, Geology of limestone near 

Gazelle, Siskiyou County, California: California Jour. Mines 

and Geology, v. 45, no. 4, p. 514-520. 
Higgins, C. G.. 1957, Pliocene rocks east of Stewart's Point, 

Sonoma County, California (abs.): Geol. Soc. America Bull., 

\. an. no. 12. pt. 2. p. 1829. 
Hinds, V I . \.. 1952, Paleozoic eruptive rocks of the southern 

Klamath Mountains, California: California Univ., Dept. (leol. 

Sci. Bull., \. 2(1. no. 11, p. T5-410. 
, 1933, Geologic formations of the Rcdding-Wcavervillc 

districts, northern California, in 29th report of the State Min- 
eralogist: California Div. Mines, v. 29, nos. 1, 2, p. 77-122. 

. 1934, The Jurassic age of the last granitoid intrusives in 

the Klamath Mountains and Sierra Nevada, California: Am. 

Jour. Sci.. ser. 5. \. 2". no. 159, p. 182-192. 

— , 1955. Meso/oic and Cenozoic eruptive rocks of the south- 
ern Klamath Mountains, California: California L'mv.. Dept. 

Geol. Sci. Bull., v. 2!. no. 11. p. 313-380. 
— , 1952. Evolution of the California landscape: California 

Div. Mines Bull. 158, 240 p. 
Holway, R. S., 1914. Apparent limits of former glaciation in the 

northern Coast Ranges of California (abs.): Geol. Soc. America 

Bull., v. 25, p. 120-121. 
Hoots. II. \Y.. 1928, Geologic map of southwestern Humboldt 

County: Oil Bull., April, p. 576. 



Irwin, AY. P., 1957, Franciscan group in Coast Ranges and its 
equivalents in Sacramento Valley, California: Am. Assoc. Pe- 
troleum Geologists Hull., v. 41, no. 10. p. 22K4-2297. 

Jenkins, O. P.. 1938, Geologic map of California: California Div. 
Mines. 6 she* i v 

Jennings. C. \\ ., ami Hart. I". W., 1956, Exploratory wells drilled 
outside of oil and gas fields in California to December 31, I 1 
California Div. Mines Special Rept. 45, 104 p. 

King, P. B., and others, 1944, Tectonic map of the United Si 
\ni. ^ssoc. Petroleum Geologists. 

Kinkel, \. R.. Jr., and Albers, J. P., 1951, Geology of the massive 
sulfide deposits at linn Mountain, Shasta County, California: 
California Div. Mines Special Rept. 14, 19 p. 

Kinkel. A. R.. Jr.. Hall, \V. I'., and Albers, J. P., 1956, Geo 
and base metal deposits of West Shasta copper-zinc district, 
Shasta County, California: U. S. Geol. Survey Prof. Paper 285, 
156 p. 

Kirby. J. M., 194'. Upper Cretaceous stratigraphy of the west side 
of Sacramento Valley south of Willows, Glenn County, Cali- 
fornia: Am. Assoc. Petroleum Geologists Bulk, v. 27, no. '. 
li. 2-9-305. 

Kiipper, Klaus, 1955, Upper Cretaceous foraminifera from the 
"Franciscan series", New Almaden district, California: Cush- 
man Found. I'oram Research Contr., v. 6, pt. 5. no. 138, p. 
112-118. 

Lawson, A. G, 1894, The gcomorphogeny of the coast of northern 
California: California Univ., Dept. Geol. Sci. Bulk, v. 1. no. 8, 
p. 241-271. 

, 1895, Sketch of the geology of the San Francisco Penin- 
sula: U. S. Geol. Survey 15th Ann. Rept., p. 399-476. 

— , 1914, Description of the San Francisco district; Tamal- 

pais, San Francisco, Concord, San Mateo, and Hayward quad- 
rangles: U. S. Geol. Survey Geol. Atlas, Folio 19!, 24 p. 

Lawson, A. C. ami others, 1908, The California earthquake of 
April 18, 1906. Report of the Sr.ue Earthquake Investigation 
Commission: Carnegie Inst. Washington Pub., no. 8", v. 1, pt. 
1. 2. and \rlas. 

Logan, C. A., 1919, Platinum and allied metals in California: Cali- 
fornia State Mining Bur. Bull. 85, 120 p. 

. 194". limestone in California: California Jour. Mines and 

Geology, v. 43, no. 3, p. 175-357. 

Louderback, G. D., 1905, The Meso/oic of southwestern Oregon: 
Jour. Geology, \. 13, p. 514-555. 

WacGinitic. II. D., 1937, The Flora of the Weaverville beds of 
Trinity County, California. ;'// Eocene flora of Western 
America: Carnegie Inst. Washington, Contr. to Paleo., Pub. 
465, p. 84-151. 

— , 1943, Central and southern Humboldt County: California 
Div. Mines Hull. lis. pt. 3, p. 633-635. 

Manning, G. A., ami Ogle. B. \.. 1950, Geology of the Blue Lake 
quadrangle, California: California Div. Mines Bull. 148, 36 p. 

Maxson, J. H., 1933, Economic geology of portions of Del None 
and Siskiyou Counties, northw esternmost California, in 29th 
report of the State Mineralogist: California Div. Mines, v. 29, 
nos. 1, 2, p. 123-160. 

Menard, II. W.. 1955, Fractures in the Pacific floor: Scientific 
American, v. 195, no. 1, p. 36-41. 

Merri.un. C. W\, 194(1. Devonian stratigraphy and paleontology 
of the Roberts Mountains region. Nevada: Geol. Soc. America 
Special Paper 25, 114 p. 

Miller, A. K., Furnish, W. M., and Clark. D. L., 1957, Permian 
Ammonoids from western United States: four. Paleontologv. v. 
51, no. 6. p. 1057-1068. 

Murphy; M. V. 1956, Lower Cretaceous stratigraphic units of 
northern California: Am. Assoc. Petroleum Geologists Bull., 
v. 40. no. '>. p. 2098-2119. 

O'Brien, J. C, 1955. Mines and mineral resources of Mendocino 
Counr>-, California: California Jour. Mines and Geologv, v. 49, 
no. 4. p. !4 _ -!98. 



80 



California Division of Mines 



[Bull. 179 



Ogle, B. A., 1951. Wildcat group in the Eel River area, Hum- 
boldt County, California (abs.): Geol. Soc. American Bull., 
vol. 62, no. 12, pt. 2, p. 1510. 

Ogle, B. A., 1955, Geology of Eel River Valley area, Humboldt 
County, California: California Div. Mines Bull. 164, 128 p. 

Olmsted, F. H., 1956, Summary of ground-water conditions in 
northwestern California, in Water resources. Appendix to 
Natural resources of northwestern California: U. S. Dept. In- 
terior, Pacific Southwest Field Committee, 93 p. 

Pacific Southwest Field Committee, 1955, Geology, mineral re- 
sources, and mineral industry, Appendix to Natural resources 
of northwestern California: U. S. Dept. Interior, 40 p. 

Peck, D. L., Imlay, R. W., and Popenoe, W. P., 1956, Upper 
Cretaceous rocks of parts of southwestern Oregon and northern 
California: Am. Assoc. Petroleum Geologists Bull., v. 40, no. 8, 
p. 1968-1984. 

Peck, J. H., Jr., 1957, Marine Pliocene fauna in northwestern 
Sonoma County, California (abs.) : Geol. Soc. America Bull., 
v. 68, no. 12, pt. 2, p. 1840-1841. 

Ransome, A. L., and Kellogg, J. L., 1939, Quicksilver resources of 
California, in 35th report of the State Mineralogist: California 
Div. Mines, v. 35, no. 4, p. 353-486. 

Rice, S. J., 1953, Reconnaissance geology of the California coastal 
area north of F'ureka (abs.) : Am. Assoc. Petroleum Geologists 
Bull., v. 37, no. 12, p. 2779. 

Rynearson, G. A., 1946, Chromite deposits of the North Elder 
Creek area, Tehama County, California: U. S. Geol. Survey 
Bull. 945-G, p. 191-210. 

Rynearson, G. A., and Smith, C. T., 1940, Chromite deposits of 
the Seiad quadrangle, Siskiyou County, California: U. S. Geol. 
Survey Bull. 922-J, p. 281-306. 

Shepard, F. P., and Emery, K. O., 1941, Submarine topography 
of the California coast; canyons and tectonic interpretation: 
Geol. Soc. America Special Paper 31, 171 p. 

Smith, J. P., 1894, The metamorphic series of Shasta County, Cali- 
fornia: Jour. Geology, v. 2, p. 588-612. 

Stauffer, C. R., 1930, The Devonian of California: California 
Univ. Dept. Geol. Sci. Bull., v. 19, no. 4, p. 81-188. 

Stewart, R. E., and Stewart, K. C, 1949, Local relationships of 
the Mollusca of the Wildcat Coast section, Humboldt County, 
California: Oreg. Dept. Geol. and Min. Industries, Bull. 36, 
pt. 8, p. 166-208. 

Stinson, M. C, 1957, Geology of the Island Mountain copper 
mine, Trinity County, California: California Jour. Mines and 
Geology, v. 53, nos. 1, 2, p. 9-33. 

Stumm, E. C, 1954, A Devonian species of Heliolites from 
Nevada: Michigan Univ. Mus. Paleontology Contr., v. 11, no. 
12, p. 223-228. 

Taliaferro, N. L., 1942, Geologic history and correlation of the 
Jurassic of southwestern Oregon and California: Geol. Soc. 
America Bull., v. 53, no. 1, p. 71-112. 

— , 1943, Franciscan-Knoxville problem: Am. Assoc. Petro- 
leum Geologists Bull., v. 27, no. 2, p. 109-219. 

Taliaferro, N. L., and Hudson, F. S., 1943, Genesis of the man- 
ganese deposits of the Coast Ranges of California: California 
Div. Mines Bull. 125, p. 217-275. 

Thalmann, H. E., 1942, Globotruncana in the Franciscan lime- 
stone, Santa Clara County, California (abs.): Geol. Soc. 
America Bull., v. 53, no. 12, pt. 2, p. 1838. 



Thalmann, H. E., 194.3, Upper Cretaceous age of the "Franciscan" 
limestone near Laytonville, Mendocino County, California 
(abs.): Geol. Soc. America Bull., v. 54, no. 12, p. 1827. 

Trask, P. D., 1950, Geologic description of the manganese de- 
posits of California: California Div. Mines Bull. 152 (Suppl. to 
Bull. 125), 378 p. 

Trask, P. D., Wilson, I. F., and Simons, F. S., 1943, Manganese 
deposits of California, a summary report in Manganese in Cali- 
fornia: California Div. Mines Bull. 125, p. 51-215. 

Treasher, R. C, 1955, Areal geology of the Coyote dam site, 
Mendocino County, California (abs.): Geol. Soc. America Bull., 
v. 66, no. 12, pt. 2, p. 1666-1667. 

Tucker, W. B., 1922a, Gold lodes of the East Fork mining district, 
Trinity County, to 18th report of the State Mineralogist: Cali- 
fornia State Mining Bur., v. 18, chap. 6, p. 270-273. 

— , 1922b, Silver lodes of the South Fork mining district, 
Shasta County, in 18th report of the State Mineralogist: Cali- 
fornia State Mining Bur., v. 18, chap. 7, p. 313-321. 

Walker, G. W., 1950, The Calera limestone in San Mateo and 
Santa Clara Counties, California: California Div. Mines Special 
Rept. 1-B, 7 p. 

Weaver, C. E., 1943, Point Arena-Fort Ross region, in Geologic 
formations and economic development of oil and gas fields of 
California: California Div. Mines Bull. 118, pt. 3, p. 628-632. 

Weaver, C. E., 1949, Geology of the Coast Ranges immediately 
north of the San Francisco Bay region, California: Geol. Soc. 
America Mem. 35, 242 p. 

Wells, F. G., 1955, Preliminary geologic map of southwestern 
Oregon: U. S. Geol. Survey Mineral Inv. Map MF 38. 

Wells, F. G, and Cater, F. W., Jr., 1950, Chromite deposits of 
Siskiyou County, California: California Div. Mines Bull. 134. 
pt. 1, chap. 2, p. 77-127. 

Wells, F. G., Cater, F. W., Jr., and Rynearson, G. A., 1946, 
Chromite deposits of Del Norte County, California: California 
Div. Mines Bull. 134, pt. 1, chap. 1, 76 p. 

Wells, F. G, Hotz, P. E., and Cater, F. W., Jr., 1949, Preliminary 
description of the geology of the Kerby quadrangle, Oregon: 
Oreg. Dept. Geol. and Min. Industries, Bull. 40, 23 p. 

Wells, F. G, Smith, C. T., Rynearson, G. A., and Livermore, 
J. S., 1949, Chromite deposits near Seiad and McGuffy Creeks, 
Siskiyou County, California: U. S. Geol. Survey Bull. 948-B, 
p. 19-62. 

Wells, F. G, and Walker, G. W., 1953, Geology of the Galice 
quadrangle, Oregon: U. S. Geol. Survey Geol. Quad. Map 
[GQ 25]. 

Wells, F. G, and others, 1939, Preliminary geologic map of the 
Medford quadrangle, Oregon: Oreg. Dept. Geol. and Min. 
Industries. 

— , 1940, Preliminary geologic map of the Grants Pass quad- 
rangle, Oregon: Oreg. Dept. Geol. and Min. Industries. 

Westman, B. J., 1947, Silurian of the Klamath .Mountain province 
(abs.): Geol. Soc. America Bull., v. 58, no. 12, pt. 2, p. 1263. 

White, C. A., 1885, On new Cretaceous fossils from California: 
U. S. Geol. Survey Bull. 22, p. 7-25. 

Williams, Howel, 1949, Geology of the Macdoel quadrangle, Cali- 
fornia: California Div. Mines Bull. 151, 78 p. 

Wilmarth, M. G., 1938, Lexicon of geologic names of the United 
States: U. S. Geol. Survey Bull. 896, pt. 1 and 2, 2396 p. 



Iv7::u "-CO 3,500 



printed in CALIFORNIA STATE PRINTING OFFICE 



— 




COLLATE : 

PIECES 



80 



California Division of Mines 



[Bull. 179 



Ogle, B. A., 1951, Wildcat group in the Eel River area, Hum- 
boldt County, California (abs.) : Geol. Soc. American Bull., 
vol. 62, no. 12, pt. 2, p. 1510. 

Ogle, B. A., 1953, Geology of Eel River Valley area, Humboldt 
County, California: California Div. Mines Bull. 164, 128 p. 

Olmsted, F. H., 1956, Summary of ground-water conditions in 
northwestern California, in Water resources, Appendix to 
Natural resources of northwestern California: U. S. Dept. In- 
terior, Pacific Southwest Field Committee, 93 p. 

Pacific Southwest Field Committee, 1955, Geology, mineral re- 
sources, and mineral industry. Appendix to Natural resources 
of northwestern California: U. S. Dept. Interior, 40 p. 

Peck, D. L., Imlay, R. W., and Popenoe, W. P., 1956, Upper 
Cretaceous rocks of parts of southwestern Oregon and northern 
California: Am. Assoc. Petroleum Geologists Bull., v. 40, no. 8, 
p. 1968-1984. 

Peck, J. H., Jr., 1957, Marine Pliocene fauna in northwestern 
Sonoma County, California (abs.): Geol. Soc. America Bull., 
v. 68, no. 12, pt. 2, p. 1840-1841. 

Ransome, A. L., and Kellogg, J. L., 1939, Quicksilver resources of 
California, in 35th report of the State Mineralogist: California 
Div. Mines, v. 35, no. 4, p. 353-486. 

Rice, S. J., 1953, Reconnaissance geology of the California coastal 
area north of Eureka (abs.) : Am. Assoc. Petroleum Geologists 
Bull., v. 37, no. 12, p. 2779. 

Rynearson, G. A., 1946, Chromite deposits of the North Elder 
Creek area, Tehama County, California: U. S. Geol. Survey 
Bull. 945-G, p. 191-210. 

Rynearson, G. A., and Smith, C. T., 1940, Chromite deposits of 
the Seiad quadrangle, Siskiyou County, California: U. S. Geol. 
Survey Bull. 922-J, p. 281-306. 

Shepard, F. P., and Emery, K. O., 1941, Submarine topography 
of the California coast; canyons and tectonic interpretation: 
Geol. Soc. America Special Paper 31, 171 p. 

Smith, J. P., 1894, The metamorphic series of Shasta County, Cali- 
fornia: Jour. Geology, v. 2, p. 588-612. 

Stauffer, C. R., 1930, The Devonian of California: California 
Univ. Dept. Geol. Sci. Bull., v. 19, no. 4, p. 81-188. 

Stewart, R. E., and Stewart, K. C, 1949, Local relationships of 
the Mollusca of the Wildcat Coast section, Humboldt County, 
California: Oreg. Dept. Geol. and Min. Industries, Bull. 36, 
pt. 8, p. 166-208. 

Stinson, M. C, 1957, Geology of the Island Mountain copper 
mine, Trinity County, California: California Jour. Mines and 
Geology, v. 53, nos. 1, 2, p. 9-33. 

Stumm, E. C, 1954, A Devonian species of Heliolites from 
Nevada: Michigan Univ. Mus. Paleontology Contr., v. 11, no. 
12, p. 223-228. 

Taliaferro, N. L., 1942, Geologic history and correlation of the 
Jurassic of southwestern Oregon and California: Geol. Soc. 
America Bull., v. 53, no. 1, p. 71-112. 

— , 1943, Franciscan-Knoxville problem: Am. Assoc. Petro- 
leum Geologists Bull., v. 27, no. 2, p. 109-219. 

Taliaferro, N. L., and Hudson, F. S., 1943, Genesis of the man- 
ganese deposits of the Coast Ranges of California: California 
Div. Mines Bull. 125, p. 217-275. 

Thalmann, H. E., 1942, Qlobotruncana in the Franciscan lime- 
stone, Santa Clara County, California (abs.): Geol. Soc. 
America Bull., v. 53, no. 12, pt. 2, p. 1838. 



Thalmann, H. E., 1943, Upper Cretaceous age of the "Franciscan" 
limestone near Laytonville, Mendocino County, California 
(abs.): Geol. Soc. America Bull., v. 54, no. 12, p. 1827. 

Trask, P. D., 1950, Geologic description of the manganese de- 
posits of California: California Div. Mines Bull. 152 (Suppl. to 
Bull. 125), 378 p. 

Trask, P. D., Wilson, I. F., and Simons, F. S., 1943, Manganese 
deposits of California, a summary report in Manganese in Cali- 
fornia: California Diy. Mines Bull. 125, p. 51-215. 

Treasher, R. C, 1955, Areal geology of the Coyote dam site, 
Mendocino County, California (abs.): Geol. Soc. America Bull., 
v. 66, no. 12, pt. 2, p. 1666-1667. 

Tucker, W. B., 1922a, Gold lodes of the East Fork mining district, 
Trinity County, hi 18th report of the State Mineralogist: Cali- 
fornia State Mining Bur., v. 18, chap. 6, p. 270-273. 

, 1922b, Silver lodes of the South Fork mining district, 

Shasta County, in 18th report of the State Mineralogist: Cali- 
fornia State Alining Bur., v. 18, chap. 7, p. 313-321. 

Walker, G. W., 1950, The Calera limestone in San Mateo and 
Santa Clara Counties, California: California Div. Alines Special 
Rept. 1-B, 7 p. 

Weaver, C. E., 1943, Point Arena-Fort Ross region, in Geologic 
formations and economic development of oil and gas fields of 
California: California Div. Alines Bull. 118, pt. 3, p. 628-632. 

Weaver, C. E., 1949, Geology of the Coast Ranges immediately 
north of the San Francisco Bay region, California: Geol. Soc. 
America Mem. 35, 242 p. 

Wells, F. G., 1955, Preliminary geologic map of southwestern 
Oregon: U. S. Geol. Survey Mineral Inv. Map AIF 38. 

Wells, F. G., and Cater, F. W., Jr., 1950, Chromite deposits of 
Siskiyou County, California: California Div. Alines Bull. 134, 
pt. 1, chap. 2, p. 77-127. 

Wells, F. G., Cater, F. W., Jr., and Rynearson, G. A., 1946, 
Chromite deposits of Del Norte County, California: California 
Div. Alines Bull. 134, pt. 1, chap. 1, 76 p. 

Wells, F. G., Hotz, P. E., and Cater, F. W., Jr., 1949, Preliminary 
description of the geology of the Kerby quadrangle, Oregon: 
Oreg. Dept. Geol. and Alin. Industries, Bull. 40, 23 p. 

Wells, F. G., Smith, C. T., Rynearson, G. A., and Livermore, 
J. S., 1949, Chromite deposits near Seiad and AIcGuffy Creeks, 
Siskiyou County, California: U. S. Geol. Survey Bull. 948-B, 
p. 19-62. 

Wells, F. G., and Walker, G. W., 195 3, Geology of the Galice 
quadrangle, Oregon: U. S. Geol. Survey Geol. Quad. A lap 
[GQ 25]. 

Wells, F. G., and others, 1939, Preliminary geologic map of the 
Medford quadrangle, Oregon: Oreg. Dept. Geol. and Alin. 
Industries. 

— , 1940, Preliminary geologic map of the Grants Pass quad- 
rangle, Oregon: Oreg. Dept. Geol. and Alin. Industries. 

Westman, B. J., 1947, Silurian of the Klamath Mountain province 
(abs.): Geol. Soc. America Bull., v. 58, no. 12, pt. 2, p. 1263. 

White, C. A., 1885, On new Cretaceous fossils from California: 
U. S. Geol. Survey Bull. 22, p. 7-25. 

Williams, Howel, 1949, Geology of the Alacdoel quadrangle, Cali- 
fornia: California Div. Alines Bull. 151, 78 p. 

Wilmarth, Al. G., 1938, Lexicon of geologic names of the United 
States: U. S. Geol. Survey Bull. 896, pt. 1 and 2, 2396 p. 



1S730 



-60 3,500 



ttiled in CALIFORN 



A STATE PRINTING OFf ICE 



t 



Foldout too large 
for digitization 



May be added at a 

later date